Trapping Rain Water

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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!

 答案

public class Solution {    public int trap(int[] A) {        if(A==null||A.length<=2)        {            return 0;        }        int N=A.length;        int []left=new int[N];        int result=0;        left[0]=A[0];        for(int index=1;index<N;index++)        {            left[index]=Math.max(left[index-1],A[index]);        }        for(int i=N-1;i>0;i--)        {            int height=Math.min(left[i-1],A[i]);            for(int j=i-1;A[j]<height;j--)            {                result+=height-A[j];                A[j]=height;            }        }        return result;    }}

ArrayStack Two Pointers

Trapping Rain Water