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Container With Most Water at Apple — Interview Guide

How to approach Container With Most Water in a Apple interview: the optimal approach, what Apple interviewers look for, and company-specific tips.

Updated 2026-09MediumTwo Pointers

The problem at Apple

Given an array of non-negative heights, find two lines that together with the x-axis form a container holding the most water. The amount is the distance between the lines times the shorter height.

Apple uses this problem to assess craft, detail, and domain depth. Expect Apple-specific follow-ups that tie the solution back to production reasoning and the company's engineering bar.

Key concepts

Width × min(height[left], height[right]) is the candidate area.
Moving the taller pointer can never increase the area (width shrinks and the limit is the shorter line).
So always move the shorter pointer inward — the only moves that can improve the answer.

Approach

Place one pointer at each end.
Compute the area; track the maximum.
Move the pointer at the shorter line inward; repeat until they meet.

def max_area(h):
    l, r, best = 0, len(h) - 1, 0
    while l < r:
        best = max(best, (r - l) * min(h[l], h[r]))
        if h[l] < h[r]:
            l += 1
        else:
            r -= 1
    return best

Complexity

Metric	Value
Time	O(n)
Space	O(1)

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