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Koko Eating Bananas

Medium

Binary search on the answer (eating speed)

In simple words

Guess an eating speed; if she finishes in time try slower, otherwise faster — narrow to the slowest speed that works.

The idea

The eating speed is monotonic: faster always finishes at least as soon. Binary search the smallest speed for which the total hours fit within h.

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candidates11

Step 1 of 6. Brute force: try every eating speed from 1 up until Koko finishes within 8 hours. Values: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11. candidates 11.

1/6
Brute force
timeO(max·n)spaceO(1)

Try every speed.

1let best = -1;2for (let k = 1; k <= maxPile && best < 0; k++)3  if (hoursNeeded(k) <= h) best = k;4return best;

Input

array
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11]

Memory

try
—
candidates
11
speed
—

Output

speed
—
answer
—

Check yourself

3 quick questions about this walkthrough. A wrong answer costs nothing.

Examples

Example 1

Input:
piles = [3, 6, 7, 11], h = 8
Output:
4
Explanation:
Eating 4 bananas/hour finishes in time.

Example 2

Input:
piles = [30, 11, 23, 4, 20], h = 5
Output:
30
Explanation:
She must eat 30/hour to finish in 5 hours.

Example 3

Input:
piles = [30, 11, 23, 4, 20], h = 6
Output:
23
Explanation:
One extra hour lets her slow to 23/hour.

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