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mediumDSA

What is binary search on the answer?

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01

Understand the problem

Explain binary searching a value range.

binary-searchsearch-space
02

Attempt it yourself

Sketch your approach before reading the solution — that's what interviews test.

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03

Study the solution

When the answer is monotonic — a candidate value either works or doesn't, with a clean threshold — you binary search over the value range instead of an array, using a feasibility check at each midpoint. Used for problems like Koko eating bananas or minimum ship capacity. O(log(range) × checkCost).

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04

Read the code

Koko eating bananas
Run Playground
def min_eating_speed(piles, hours):
    def hours_needed(speed):
        return sum((p + speed - 1) // speed for p in piles)   # ceil division
    lo, hi = 1, max(piles)
    while lo < hi:
        mid = (lo + hi) // 2
        if hours_needed(mid) <= hours:
            hi = mid             # feasible — try slower
        else:
            lo = mid + 1         # too slow — speed up
    return lo


# --- demo ---
print(min_eating_speed([3, 6, 7, 11], 8))        # 4
print(min_eating_speed([30, 11, 23, 4, 20], 5))  # 30
05

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