LeetCode 1093: Statistics from a Large Sample
A clear explanation of computing statistical measures (minimum, maximum, mean, median, mode) from a frequency count array.
Tag
Math
171 notes
LeetCode 1088: Confusing Number II
A clear explanation of counting confusing numbers up to n using digit backtracking with rotation validation.
LeetCode 1085: Sum of Digits in the Minimum Number
A clear explanation of checking if the digit sum of the array minimum is odd or even.
LeetCode 1073: Adding Negative Numbers
A clear explanation of adding two non-positive integers represented as arrays of digits.
LeetCode 1071: Greatest Common Divisor of Strings
A clear explanation of finding the longest string that divides both strings using the GCD of their lengths.
LeetCode 1067: Digit Count in Range
A clear explanation of counting the occurrences of a specific digit in all numbers from 1 to n using digit dynamic programming.
LeetCode 1058: Minimize Rounding Error to Meet Target
A clear explanation of minimizing total rounding error when rounding prices to meet a target sum using a greedy approach.
LeetCode 1056: Confusing Number
A clear explanation of checking if a number becomes a different valid number when rotated 180 degrees.
LeetCode 1041: Robot Bounded In Circle
A clear explanation of determining if a robot stays in a bounded circle by checking position and direction after one instruction cycle.
LeetCode 1040: Moving Stones Until Consecutive II
A clear explanation of finding minimum and maximum moves to make stones consecutive using a sliding window.
LeetCode 1037: Valid Boomerang
A clear explanation of checking if three points form a boomerang (non-collinear) using the cross product.
LeetCode 1033: Moving Stones Until Consecutive
A clear explanation of finding the minimum and maximum moves to make three stones consecutive by analyzing gap cases.
LeetCode 1030: Matrix Cells in Distance Order
A clear explanation of sorting matrix cells by Chebyshev distance from a given center cell using BFS.
LeetCode 1025: Divisor Game
A clear explanation of why Alice wins the divisor game if and only if n is even, proven by mathematical induction.
LeetCode 1017: Convert to Base -2
A clear explanation of converting a non-negative integer to its base negative-two representation.
LeetCode 1015: Smallest Integer Divisible by K
A clear explanation of finding the smallest repunit divisible by K by tracking remainders to detect cycles.
LeetCode 1012: Numbers With Repeated Digits
A clear explanation of counting numbers up to n with at least one repeated digit using digit DP and combinatorics.
LeetCode 1006: Clumsy Factorial
A clear explanation of computing the clumsy factorial by simulating cyclic operators with a stack.
LeetCode 964: Least Operators to Express Number
A clear explanation of expressing a target using the fewest operators with repeated uses of x.
LeetCode 612: Shortest Distance in a Plane
A SQL guide for finding the minimum Euclidean distance between any two points in a 2D plane.
LeetCode 523: Continuous Subarray Sum
A clear explanation of detecting a subarray whose sum is a multiple of k using prefix sums and modular arithmetic.
LeetCode 507: Perfect Number
A clear explanation of checking whether a number equals the sum of its positive divisors excluding itself.
LeetCode 504: Base 7
A clear explanation of converting an integer into its base 7 string representation using repeated division.
LeetCode 413: Arithmetic Slices
A clear explanation of counting arithmetic subarrays using dynamic programming and consecutive differences.
LeetCode 372: Super Pow
A clear explanation of computing large modular exponentiation using fast power, modular arithmetic, and digit decomposition.
LeetCode 342: Power of Four
A clear explanation of Power of Four using bit manipulation and binary properties.
LeetCode 233: Number of Digit One
A detailed explanation of counting how many times digit one appears from 0 to n using positional digit analysis.
LeetCode 231: Power of Two
A clear explanation of determining whether an integer is a power of two using binary properties and bit manipulation.
LeetCode 172: Factorial Trailing Zeroes
A clear explanation of counting trailing zeroes in n! by counting factors of 5 instead of computing the factorial directly.
LeetCode 171: Excel Sheet Column Number
A clear explanation of converting an Excel column title into its numeric index using base 26 accumulation.
LeetCode 150: Evaluate Reverse Polish Notation
Evaluate an arithmetic expression written in Reverse Polish Notation using a stack.
LeetCode 149: Max Points on a Line
Find the maximum number of points lying on the same straight line using slope counting and normalization.
LeetCode 142: Linked List Cycle II
Find the node where a linked list cycle begins using Floyd’s tortoise and hare algorithm with cycle entry mathematics.
LeetCode 119: Pascal's Triangle II
A clear explanation of generating a single row of Pascal's Triangle using in-place dynamic programming.
LeetCode 118: Pascal's Triangle
A clear explanation of generating Pascal's Triangle row by row using dynamic programming.
LeetCode 973: K Closest Points to Origin
A clear explanation of returning the k closest points to the origin using squared distance and sorting.
LeetCode 972: Equal Rational Numbers
A clear explanation of comparing rational numbers written as decimal strings with optional repeating parts.
LeetCode 970: Powerful Integers
A clear explanation of generating all powerful integers using bounded powers and a set.
LeetCode 963: Minimum Area Rectangle II
A clear explanation of finding the minimum-area rectangle from points when the rectangle may be rotated.
LeetCode 952: Largest Component Size by Common Factor
A clear explanation of solving Largest Component Size by Common Factor using prime factorization and union find.
LeetCode 837: New 21 Game
A clear explanation of the New 21 Game problem using probability dynamic programming and a sliding window sum.
LeetCode 836: Rectangle Overlap
A clear explanation of the Rectangle Overlap problem using axis projections and positive intersection area.
LeetCode 829: Consecutive Numbers Sum
A clear explanation of the Consecutive Numbers Sum problem using arithmetic series formulas and divisibility analysis.
LeetCode 920: Number of Music Playlists
A clear explanation of counting valid music playlists using dynamic programming over playlist length and unique songs used.
LeetCode 914: X of a Kind in a Deck of Cards
A clear explanation of checking whether card counts share a common group size using the greatest common divisor.
LeetCode 908: Smallest Range I
A clear explanation of minimizing an array score after each value can move by at most k.
LeetCode 906: Super Palindromes
A clear explanation of counting super-palindromes by generating palindromic roots and checking their squares.
LeetCode 902: Numbers At Most N Given Digit Set
A clear explanation of counting numbers less than or equal to N using digit-by-digit construction and combinatorics.
LeetCode 899: Orderly Queue
A clear explanation of finding the lexicographically smallest string after queue operations using rotation and sorting.
LeetCode 892: Surface Area of 3D Shapes
A clear explanation of computing the exposed surface area of stacked cubes by adding tower area and subtracting shared faces.
LeetCode 891: Sum of Subsequence Widths
A clear explanation of summing subsequence widths by sorting and counting each element as a maximum and minimum.
LeetCode 888: Fair Candy Swap
A clear explanation of finding one candy box swap that makes Alice and Bob have equal total candies.
LeetCode 887: Super Egg Drop
A clear explanation of finding the minimum worst-case number of moves using dynamic programming over eggs and moves.
LeetCode 880: Decoded String at Index
A clear explanation of finding the kth character in a decoded string without building the full decoded string.
LeetCode 878: Nth Magical Number
A clear explanation of finding the nth magical number using binary search, greatest common divisor, least common multiple, and inclusion-exclusion.
LeetCode 625: Minimum Factorization
A clear explanation of Minimum Factorization using greedy digit factors from 9 down to 2.
LeetCode 991: Broken Calculator
A clear explanation of finding the minimum operations by working backward from target to startValue.
LeetCode 989: Add to Array-Form of Integer
A clear explanation of adding an integer to an array-form number using digit-by-digit simulation.
LeetCode 869: Reordered Power of 2
A clear explanation of checking whether the digits of a number can be reordered to form a power of two using digit frequency signatures.
LeetCode 866: Prime Palindrome
A clear explanation of finding the smallest prime palindrome greater than or equal to n by generating odd-length palindromes and testing primality.
LeetCode 858: Mirror Reflection
A clear explanation of Mirror Reflection using room unfolding, least common multiples, and parity.
LeetCode 932: Beautiful Array
A clear explanation of solving Beautiful Array using divide and conquer with odd and even transformations.
LeetCode 818: Race Car
A dynamic programming solution for finding the shortest instruction sequence that drives a race car to the target position.
LeetCode 812: Largest Triangle Area
A geometry solution for finding the largest triangle area by checking every triplet of points with the cross product formula.
LeetCode 810: Chalkboard XOR Game
A math and bit manipulation solution for deciding whether Alice wins the XOR removal game.
LeetCode 805: Split Array With Same Average
A dynamic programming solution for deciding whether an array can be split into two non-empty groups with the same average.
LeetCode 800: Similar RGB Color
A clear explanation of finding the closest shorthand RGB color by rounding each color channel to the nearest repeated hexadecimal pair.
LeetCode 793: Preimage Size of Factorial Zeroes Function
A clear explanation of finding how many integers have exactly k trailing zeroes in their factorial.
LeetCode 790: Domino and Tromino Tiling
A clear explanation of counting tilings of a 2 x n board using dominoes and L-shaped trominoes with dynamic programming.
LeetCode 789: Escape The Ghosts
A clear explanation of deciding whether escape is possible by comparing Manhattan distances to the target.
LeetCode 788: Rotated Digits
A clear explanation of counting good numbers after rotating every digit by 180 degrees.
LeetCode 782: Transform to Chessboard
A clear explanation of transforming a binary board into a chessboard using feasibility checks and minimum row and column swaps.
LeetCode 781: Rabbits in Forest
A clear explanation of finding the minimum possible number of rabbits using counting and greedy grouping.
LeetCode 780: Reaching Points
A clear explanation of checking whether one point can reach another by working backward with modulo.
LeetCode 779: K-th Symbol in Grammar
A clear explanation of finding the kth symbol in the grammar sequence using recursion and the parent-child relationship.
LeetCode 775: Global and Local Inversions
A clear explanation of checking whether every global inversion is also a local inversion using distance constraints.
LeetCode 770: Basic Calculator IV
A clear explanation of simplifying algebraic expressions by parsing, substituting variables, and combining polynomial terms.
LeetCode 762: Prime Number of Set Bits in Binary Representation
A clear explanation of counting numbers whose binary representation has a prime number of set bits.
LeetCode 754: Reach a Number
A clear explanation of reaching a target on a number line using cumulative sums and parity.
LeetCode 710: Random Pick with Blacklist
A clear explanation of selecting a uniformly random integer while excluding blacklisted values using remapping and hashing.
LeetCode 738: Monotone Increasing Digits
Find the largest number less than or equal to n whose digits are monotone increasing using a greedy digit adjustment.
LeetCode 728: Self Dividing Numbers
Check each number in a range by extracting its digits and testing whether every digit divides the original number.
LeetCode 679: 24 Game
Determine whether four numbers can be combined with arithmetic operations and parentheses to produce 24.
LeetCode 672: Bulb Switcher II
A clear explanation of counting possible bulb states after pressing four toggle buttons exactly presses times.
LeetCode 670: Maximum Swap
A clear explanation of maximizing an integer by swapping at most two digits once.
LeetCode 668: Kth Smallest Number in Multiplication Table
A clear explanation of finding the kth smallest value in an m by n multiplication table using binary search on answer.
LeetCode 651: 4 Keys Keyboard
A dynamic programming solution for maximizing the number of A characters printed with a limited number of keyboard operations.
LeetCode 650: 2 Keys Keyboard
A dynamic programming and prime factorization solution for finding the minimum operations needed to produce n characters.
LeetCode 645: Set Mismatch
A counting and math solution for finding the duplicated number and the missing number in a corrupted set.
LeetCode 640: Solve the Equation
A string parsing solution for reducing a linear equation into coefficient and constant terms.
LeetCode 634: Find the Derangement of An Array
A dynamic programming and combinatorics solution for counting permutations with no fixed positions.
LeetCode 633: Sum of Square Numbers
A two-pointer and number theory solution for checking whether an integer can be written as the sum of two square numbers.
LeetCode 629: K Inverse Pairs Array
A dynamic programming solution for counting permutations of 1 to n with exactly k inverse pairs.
LeetCode 628: Maximum Product of Three Numbers
A clear explanation of finding the largest product of three numbers using sorting or constant-space tracking.
LeetCode 227: Basic Calculator II
A detailed explanation of evaluating arithmetic expressions with stack-based parsing and operator precedence.
LeetCode 50: Pow(x, n)
A clear explanation of Pow(x, n) using binary exponentiation to compute powers in logarithmic time.
LeetCode 48: Rotate Image
A clear explanation of Rotate Image using in-place matrix transpose and row reversal.
LeetCode 43: Multiply Strings
A clear explanation of Multiply Strings using grade-school multiplication with digit arrays.
LeetCode 660: Remove 9
A clear explanation of finding the nth positive integer that does not contain the digit 9 using base-9 conversion.
LeetCode 610: Triangle Judgement
A SQL guide for checking whether three side lengths can form a valid triangle using the triangle inequality.
LeetCode 598: Range Addition II
A clear math solution for counting the maximum values after repeated top-left matrix increment operations.
LeetCode 593: Valid Square
A clear geometry solution for checking whether four unordered points form a valid square.
LeetCode 592: Fraction Addition and Subtraction
A clear parsing and math solution for evaluating fraction addition and subtraction expressions.
LeetCode 573: Squirrel Simulation
A clear explanation of Squirrel Simulation using Manhattan distance and the special first trip.
LeetCode 564: Find the Closest Palindrome
A clear explanation of Find the Closest Palindrome using prefix mirroring and a small candidate set.
LeetCode 556: Next Greater Element III
A clear explanation of Next Greater Element III using the next permutation algorithm on the digits of an integer.
LeetCode 553: Optimal Division
A clear explanation of Optimal Division using the structure of division expressions to build the maximum-value expression.
LeetCode 537: Complex Number Multiplication
A clear explanation of multiplying complex numbers represented as strings using algebraic expansion.
LeetCode 509: Fibonacci Number
A clear explanation of computing Fibonacci numbers using dynamic programming and iterative state transitions.
LeetCode 492: Construct the Rectangle
A clear explanation of finding rectangle dimensions with a fixed area and the smallest length-width difference.
LeetCode 483: Smallest Good Base
A clear explanation of finding the smallest base where n is written as all ones using geometric series and binary search.
LeetCode 479: Largest Palindrome Product
A clear explanation of finding the largest palindrome made from the product of two n-digit numbers by generating palindrome candidates directly.
LeetCode 478: Generate Random Point in a Circle
A clear explanation of generating uniformly random points inside a circle using polar coordinates.
LeetCode 470: Implement Rand10() Using Rand7()
A clear explanation of generating a uniform random integer from 1 to 10 using only rand7 and rejection sampling.
LeetCode 469: Convex Polygon
A clear explanation of checking whether ordered points form a convex polygon using cross products.
LeetCode 462: Minimum Moves to Equal Array Elements II
A clear explanation of why the median minimizes the number of moves needed to make all array elements equal.
LeetCode 458: Poor Pigs
A clear explanation of the combinatorics behind finding the minimum number of pigs needed to identify the poisonous bucket.
LeetCode 453: Minimum Moves to Equal Array Elements
A clear explanation of the math behind making all array elements equal by incrementing n - 1 elements at a time.
LeetCode 447: Number of Boomerangs
Count ordered boomerang tuples by fixing each point as the center and grouping other points by squared distance.
LeetCode 445: Add Two Numbers II
Add two numbers stored in forward-order linked lists using stacks and carry propagation.
LeetCode 441: Arranging Coins
Find the maximum number of complete staircase rows that can be formed using binary search and triangular numbers.
LeetCode 440: K-th Smallest in Lexicographical Order
Find the k-th integer in lexicographical order without generating all numbers, using prefix counting over a conceptual trie.
LeetCode 415: Add Strings
A clear explanation of adding two non-negative integer strings using manual digit-by-digit simulation.
LeetCode 412: Fizz Buzz
A clear explanation of the Fizz Buzz problem using direct simulation and divisibility checks.
LeetCode 405: Convert a Number to Hexadecimal
A clear explanation of converting integers to hexadecimal using bit manipulation and two's complement representation.
LeetCode 400: Nth Digit
A clear explanation of finding the nth digit in the infinite integer sequence using digit groups and arithmetic.
LeetCode 398: Random Pick Index
A clear explanation of picking a uniformly random index for a target value using reservoir sampling, with an alternative hash map approach.
LeetCode 397: Integer Replacement
A clear explanation of reducing an integer to 1 with the fewest operations using greedy bit decisions.
LeetCode 396: Rotate Function
A clear explanation of maximizing the rotation function using a recurrence instead of simulating every rotation.
LeetCode 390: Elimination Game
A clear explanation of finding the last remaining number after alternating left-to-right and right-to-left eliminations.
LeetCode 384: Shuffle an Array
A clear explanation of shuffling an array uniformly using the Fisher-Yates algorithm while supporting reset.
LeetCode 382: Linked List Random Node
A clear explanation of selecting a random linked list node with equal probability using reservoir sampling.
LeetCode 371: Sum of Two Integers
A clear explanation of adding two integers without using plus or minus by using XOR, AND, carry, and a 32-bit mask.
LeetCode 369: Plus One Linked List
A clear explanation of adding one to a number stored as a linked list using the rightmost non-nine digit.
LeetCode 368: Largest Divisible Subset
A clear explanation of finding the largest subset where every pair is divisible using sorting, dynamic programming, and parent reconstruction.
LeetCode 367: Valid Perfect Square
A clear explanation of checking whether an integer is a perfect square using binary search without sqrt.
LeetCode 365: Water and Jug Problem
A clear explanation of solving the Water and Jug Problem using Bézout's identity and greatest common divisor.
LeetCode 360: Sort Transformed Array
A clear explanation of sorting values after applying a quadratic function using two pointers.
LeetCode 357: Count Numbers with Unique Digits
A clear explanation of counting numbers with unique digits using combinatorics.
LeetCode 343: Integer Break
A clear explanation of Integer Break using dynamic programming, with a note on the greedy math solution.
LeetCode 335: Self Crossing
A clear explanation of Self Crossing using constant-space checks for the only possible crossing patterns.
LeetCode 326: Power of Three
A clear explanation of the Power of Three problem using repeated division and integer arithmetic.
LeetCode 319: Bulb Switcher
A clear explanation of Bulb Switcher using divisor parity and perfect squares.
LeetCode 313: Super Ugly Number
A clear explanation of Super Ugly Number using dynamic programming with one pointer per prime.
LeetCode 296: Best Meeting Point
A median-based solution for minimizing total Manhattan distance in a grid.
LeetCode 292: Nim Game
A game theory solution for deciding whether the first player can win by using the losing-position pattern of multiples of four.
LeetCode 279: Perfect Squares
A dynamic programming solution for finding the least number of perfect square numbers that sum to n.
LeetCode 273: Integer to English Words
A clear explanation of the Integer to English Words problem using three-digit chunks and scale words.
LeetCode 268: Missing Number
A clear explanation of the Missing Number problem using sum formula and XOR.
LeetCode 264: Ugly Number II
A clear explanation of the Ugly Number II problem using dynamic programming with three pointers.
LeetCode 263: Ugly Number
A clear explanation of the Ugly Number problem using repeated division by the only allowed prime factors.
LeetCode 258: Add Digits
A clear explanation of the Add Digits problem using repeated digit sums first, then the digital root formula.
LeetCode 254: Factor Combinations
A clear explanation of the Factor Combinations problem using DFS backtracking with non-decreasing factors.
LeetCode 223: Rectangle Area
A clear explanation of computing the total covered area of two axis-aligned rectangles by subtracting their overlap.
LeetCode 204: Count Primes
A clear explanation of counting prime numbers less than n using the Sieve of Eratosthenes.
LeetCode 202: Happy Number
A clear explanation of detecting whether repeated digit-square sums eventually reach 1.
LeetCode 96: Unique Binary Search Trees
A detailed guide to solving Unique Binary Search Trees with dynamic programming and the Catalan recurrence.
LeetCode 89: Gray Code
A detailed guide to solving Gray Code using the binary-to-Gray-code formula.
LeetCode 168: Excel Sheet Column Title
A clear explanation of converting a positive integer into an Excel column title using bijective base 26.
LeetCode 166: Fraction to Recurring Decimal
A clear explanation of converting a fraction into decimal form and detecting repeating fractional parts with a hash map.
LeetCode 70: Climbing Stairs
A clear guide to counting distinct ways to climb stairs using dynamic programming.
LeetCode 69: Sqrt(x)
A clear guide to computing the integer square root using binary search without built-in exponent functions.
LeetCode 67: Add Binary
A clear guide to adding two binary strings using two pointers and a carry.
LeetCode 66: Plus One
A clear guide to adding one to a large integer represented as an array of digits.
LeetCode 60: Permutation Sequence
A clear guide to finding the kth permutation sequence using factorial blocks instead of generating all permutations.
LeetCode 29: Divide Two Integers
A clear explanation of integer division without using multiplication, division, or modulo, using repeated doubling with bit shifts.
LeetCode 13: Roman to Integer
A detailed explanation of converting a Roman numeral string into an integer using symbol values and the subtraction rule.
LeetCode 12: Integer to Roman
A detailed explanation of converting an integer into a Roman numeral using a fixed value-symbol table and greedy subtraction.
LeetCode 9: Palindrome Number
A detailed explanation of checking whether an integer is a palindrome using digit operations without converting it to a string.
LeetCode 7: Reverse Integer
A detailed explanation of reversing a signed 32-bit integer while handling overflow correctly.
LeetCode 2: Add Two Numbers
A detailed explanation of the Add Two Numbers linked list problem, including digit-by-digit addition, carry handling, and linked list construction.