[leetcode刷题系列]Trapping Rain Water

- - 嗯， 水题

const int MAXN = 1e6 + 10;

int dleft[MAXN], dright[MAXN];

class Solution {
public:
    int trap(int A[], int n) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        if(n <= 0)
            return 0;
        dleft[0] = 0;
        for(int i = 1; i < n; ++ i)
            dleft[i] = max(dleft[i - 1], A[i - 1]);
        dright[n - 1] = 0;
        for(int i = n - 2; i >= 0; -- i)
            dright[i] = max(dright[i + 1], A[i + 1]);
        int ans = 0;
        for(int i = 0; i < n; ++ i){
            int cur = min(dleft[i],dright[i]);
            if(cur > A[i])
                ans += cur - A[i];
        }
        return ans;
    }
};