(双指针) $O(n)$

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时间复杂度

参考文献

C++ 代码

class Solution {
public:
    int trap(vector<int>& height) {
        int len = height.size();
        if(len <= 1)
            return 0;
        int ret = 0;
        int left = 0, right = len - 1;
        int minval = 0;
        while(left < right)
        {
            minval = min(height[left], height[right]);
            while(left < right && height[left] <= minval)
            {
                ret += minval - height[left];
                ++left;
            }

            while(left < right && height[right] <= minval)
            {
                ret += minval - height[right];
                --right;
            }
        }

        return ret;
    }
};