LeetCode 42 - Trapping Rain Water

题目

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 can trap after raining.

Example 1:
Input: height = [0,1,0,2,1,0,1,3,2,1,2,1]
Output: 6
Explanation: The above elevation map (black section) 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.

思路

代码

class Solution {
public:
    int trap(vector<int>& height) {
        int left = 0, right = height.size() - 1;
        int leftMax = 0, rightMax = 0;

        int res = 0;

        while(left < right){
            if(height[left] < height[right]){
                if(height[left] >= leftMax){
                    leftMax = height[left];
                } else {
                    res += leftMax - height[left];
                }
                left++;
            } else {
                if(height[right] >= rightMax){
                    rightMax = height[right];
                } else {
                    res += rightMax - height[right];
                }
                right--;
            }
        }

        return res;
    }
};