LeetCode 1093: Statistics from a Large Sample

Problem Restatement

We are given a sample of integers. The sample is represented as a count array count where count[k] is the number of times integer k appears.

We need to compute:

minimum: the minimum value in the sample.
maximum: the maximum value in the sample.
mean: the average value, as a floating-point number.
median: the middle value (or average of two middle values if even count).
mode: the most frequent value (smallest if tie).

Return an array [minimum, maximum, mean, median, mode].

The official constraints state that count.length == 256 and the total count is between 1 and 10^4.

Input and Output

Item	Meaning
Input	Count array `count` (length 256)
Output	`[minimum, maximum, mean, median, mode]`

Function shape:

def sampleStats(count: list[int]) -> list[float]:
    ...

Examples

Example 1:

count = [0,1,3,4,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0]

Values: 1 appears once, 2 appears 3 times, 3 appears 4 times.

Min=1, Max=3, Mean=(1+6+12)/8=19/8=2.375, Mode=3 (most frequent), Median=middle of [1,2,2,2,3,3,3,3] = (2+3)/2=2.5.

Answer:

[1.0, 3.0, 2.375, 2.5, 3.0]

Edge Cases

Check the minimum input size allowed by the constraints.
Verify duplicate values or tie cases if the input can contain them.
Keep the return value aligned with the exact failure case in the statement.

Common Pitfalls

Do not optimize away the invariant; the code should still make it clear what condition is being maintained.
Prefer problem-specific names over one-letter variables once the logic becomes stateful.

Implementation

class Solution:
    def sampleStats(self, count: list[int]) -> list[float]:
        n = sum(count)
        minimum = next(i for i, c in enumerate(count) if c > 0)
        maximum = next(i for i, c in enumerate(reversed(count)) if c > 0)
        maximum = 255 - maximum

        total = sum(i * c for i, c in enumerate(count))
        mean = total / n

        mode = max(range(256), key=lambda i: count[i])

        lo, hi = (n + 1) // 2, (n + 2) // 2
        med1 = med2 = None
        running = 0
        for i, c in enumerate(count):
            running += c
            if med1 is None and running >= lo:
                med1 = i
            if med2 is None and running >= hi:
                med2 = i
                break
        median = (med1 + med2) / 2.0

        return [float(minimum), float(maximum), mean, median, float(mode)]

Testing

def run_tests():
    s = Solution()

    count = [0] * 256
    count[1] = 1; count[2] = 3; count[3] = 4
    result = s.sampleStats(count)
    assert result == [1.0, 3.0, 2.375, 2.5, 3.0]

    print("all tests passed")

run_tests()

Test	Expected	Why
`count[1]=1,count[2]=3,count[3]=4`	`[1,3,2.375,2.5,3]`	Standard statistics computation