FAANG · LeetCode #875

Koko Eating Bananas — three-stage drill

1The ProblemMedium

Koko Eating Bananas

Smallest eating speed to finish all banana piles within h hours.

Examples

piles=[3,6,7,11], h=8→ 4piles=[30,11,23,4,20], h=5→ 30

constraintAnswer (speed) lies in [1, max pile]; feasibility is monotonic.

2The PatternTIME O(log n) · SPACE O(1)

Binary Search

Halve the search space each step — check the middle, keep the half that can hold the answer.

Problems using this pattern

3The SolutionRESULT → 4

Step through it

search the eating speed in [1, 11]. h = 8 hours

Step 1 / 6

Python▎binary-search the answer (speed)

1import math
2def minEatingSpeed(piles, h):
3    left, right = 1, max(piles)
4    while left < right:
5        mid = (left + right) // 2
6        hours = sum(math.ceil(p / mid) for p in piles)
7        if hours <= h:
8            right = mid          # feasible → try slower
9        else:
10            left = mid + 1       # too slow → faster
11    return left

why it worksThere's no array to search — we binary-search the ANSWER. Speeds 1..max(piles) are the candidates, and 'can finish in h hours?' is monotonic: if a speed works, every faster speed works too. So we binary-search for the smallest speed that's still feasible.

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Koko Eating Bananas — three-stage drill