Explain Container With Most Water.

Short answer: Two pointers at both ends. Area = min(height[L], height[R]) * (R − L). Move the pointer at the shorter line inward, because width shrinks and only a taller line can improve area. O(n) time.

Complexity

Time O(n), Space O(1).

Edge cases to mention

• Length 2
• Strictly increasing heights

Common follow-ups

• Trapping Rain Water (harder, needs prefix max or stack)

Prove the greedy move: the shorter side is the bottleneck.