Algorithms-Data-Structures/trapping rainwater.cpp at main · avastino7/Algorithms-Data-Structures · GitHub

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/*
Given n non-negative integers representing an elevation map where the width of each bar is 1, compute how much water it can trap after raining.
*/

class Solution { // 0 ms, faster than 100.00%
    public int trap(int[] height) {
        if (height.length <= 2) return 0;
        int n = height.length, maxLeft = height[0], maxRight = height[n-1];
        int left = 1, right = n - 2, ans = 0;
        while (left <= right) {
            if (maxLeft < maxRight) {
                if (height[left] > maxLeft)
                    maxLeft = height[left];
                else
                    ans += maxLeft - height[left];
                left += 1;
            } else {
                if (height[right] > maxRight)
                    maxRight = height[right];
                else
                    ans += maxRight - height[right];
                right -= 1;
            }
        }
        return ans;
    }
}