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LeetCode 41 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:这道题和https://oj.leetcode.com/problems/candy/有点像,分别使用leftmax[A.length]和rightmax[A.length]来存储A[i]左边的最大值和A[i]右边的最大值。
当A[i]<Math.min(leftmax[i], rightmax[i]);时,则第i个位置是可以存储水的,否则就不能存储水。
public class Solution {
	public int trap(int[] A) {
		int result = 0,temp;
		int []leftmax=new int [A.length];
		int []rightmax=new int [A.length];
		for(int i=0,max=-1;i<A.length;i++){
			leftmax[i]=max;
			max=max>A[i]? max:A[i];
		}
		for(int i=A.length-1,max=-1;0<=i;i--){
			rightmax[i]=max;
			max=max>A[i]? max:A[i];	
		}
		for(int i=1;i<A.length-1;i++){
			temp=Math.min(leftmax[i], rightmax[i]);
			if(temp>A[i]){
				result+=temp-A[i];
			}
		}
		return result;
	}
}


LeetCode 41 Trapping Rain Water