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$ curl repovive.com/roadmaps/data-structures/stacks-monotonic-stacks/trapping-water-implementation

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$ curl repovive.com/roadmaps/data-structures/stacks-monotonic-stacks/trapping-water-implementation

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Trapping Water - Implementation - Stacks & Monotonic Stacks | Data Structures | Repovive

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Data Structures19 sections · 729 units49h total

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Trapping Water - Implementation

Complete solution

Here's the stack solution:

function trap(height)
    stack := empty stack  // stores indices
    water := 0

    for i from 0 to length of height - 1
        while stack is not empty and height[i] > height[top of stack]
            mid := pop from stack
            if stack is empty
                break  // no left boundary
            left := top of stack
            width := i - left - 1
            h := min(height[i], height[left]) - height[mid]
            water := water + width × h
        push i onto stack

    return water

Time: $O(n)$ . Space: $O(n)$ .