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!

思路：
从两边往中间搜索

class Solution {    public int trap(int[] height) {        int secHight = 0;          int left = 0;          int right = height.length-1;          int area = 0;          while (left < right){              if (height[left] <height[right]){                  secHight = Math.max(height[left], secHight);                  area += secHight-height[left];//计算当前格的能装雨水的容量                  left++;              } else {                  secHight = Math.max(height[right], secHight);                  area += secHight-height[right];                  right--;              }          }          return area;      }}