LeetCode 150: Evaluate Reverse Polish Notation
Evaluate an arithmetic expression written in Reverse Polish Notation using a stack.
Tag
Medium
17 notes
LeetCode 146: LRU Cache
Design an LRU cache with O(1) get and put operations using a hash map and doubly linked list.
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 138: Copy List with Random Pointer
Create a deep copy of a linked list with next and random pointers using hash maps or interleaved node cloning.
LeetCode 137: Single Number II
Find the number that appears once when every other number appears three times using bit counting or finite-state bit manipulation.
LeetCode 201: Bitwise AND of Numbers Range
A clear explanation of finding the bitwise AND of every number in an inclusive range using the common binary prefix.
LeetCode 148: Sort List
Sort a singly linked list in ascending order using merge sort with fast and slow pointers.
LeetCode 147: Insertion Sort List
Sort a singly linked list using insertion sort by splicing each node into a growing sorted list.
LeetCode 143: Reorder List
Reorder a singly linked list in-place by finding the middle, reversing the second half, and merging the two halves alternately.
LeetCode 139: Word Break
Decide whether a string can be segmented into dictionary words using dynamic programming over prefixes.
LeetCode 134: Gas Station
Find the unique starting gas station index using a greedy scan with total fuel balance and current tank balance.
LeetCode 133: Clone Graph
Create a deep copy of a connected undirected graph using DFS and a hash map from original nodes to cloned nodes.
LeetCode 131: Palindrome Partitioning
Generate all ways to split a string so that every piece is a palindrome, using backtracking with palindrome precomputation.
LeetCode 130: Surrounded Regions
Capture surrounded O regions by marking border-connected O cells first, then flipping the remaining O cells.
LeetCode 129: Sum Root to Leaf Numbers
Compute the sum of all numbers formed by root-to-leaf paths using depth-first search and decimal accumulation.
LeetCode 128: Longest Consecutive Sequence
Find the longest run of consecutive integers in an unsorted array using a hash set and sequence-start detection.
LeetCode 127: Word Ladder
Use breadth-first search to find the shortest transformation sequence length between two words.