LeetCode 41 Trapping Rain Water

標籤：java   leetcode   

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：這道題和https://oj.leetcode.com/problems/candy/有點像，分別使用leftmax[A.length]和rightmax[A.length]來儲存A[i]左邊的最大值和A[i]右邊的最大值。當A[i]<Math.min(leftmax[i], rightmax[i]);時，則第i個位置是可以儲存水的，否則就不能儲存水。

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