# leetcode 42. Trapping Rain Water

Use first for loop to find highest bar and its id. Then trace from left and right to this id individually.

class Solution {
public:
    int trap(vector<int>& height) {
        int max = -1, max_id, cur_hei = 0, res = 0, size = height.size();
        for(int i = 0; i < size; i++){
            if(height[i] > max){
                max = height[i];
                max_id = i;
            }
        }        
        for(int i = 0; i < max_id; i++){
            if(height[i] > cur_hei) 
                cur_hei = height[i];
            else 
                res += cur_hei - height[i];
        }
        cur_hei = 0;
        for(int i = size - 1; i > max_id; i--){
            if(height[i] > cur_hei)
                cur_hei = height[i];
            else
                res += cur_hei - height[i];
        }
        
        return res;
    }
};

###### tags: `leetcode` `c++`