[hard]42. Trapping Rain Water

最新推荐文章于 2021-05-14 23:03:36 发布

原创最新推荐文章于 2021-05-14 23:03:36 发布 · 215 阅读

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本文介绍了一个经典的算法问题——雨水收集。通过给定的地形高度数组，利用双指针技巧计算地形能够承载多少雨水。该算法首先找到左右两边的最高点，并依据较低一侧的高度来累积雨水量。

42. Trapping Rain Water

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

For example,
Given [0,1,0,2,1,0,1,3,2,1,2,1], return 6.

The above elevation map is represented by array [0,1,0,2,1,0,1,3,2,1,2,1]. In this case, 6 units of rain water (blue section) are being trapped. Thanks Marcos for contributing this image!

Solution:

class Solution {
public:
    int trap(vector<int>& height) {
        if (height.size() == 0)
            return 0;
        int res = 0;
        size_t l = 0, r = height.size() - 1;
        while(l < r) {
            int minh = min(height[l], height[r]);
            while(l < r && height[l] <= minh)
                res += minh, ++ l;
            while(l < r && height[r] <= minh)
                res += minh, -- r;
        }
        res += height[l];
        return res - accumulate(height.begin(), height.end(), 0);
    }
};