标签：style blog http io color ar os sp for
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!
Analysis:
We scan the whole array twice. First: from head to end; Second: from end to start.
In every scan, we record the current bar for rain trapping. If the value of current column is less than the bar, then current store += bar-currentValueOfColumn; Else, current store is end, we then add the current store into the total store, and reset the bar as currentValueOfColumn.
Solution:
1 public class Solution { 2 public int trap(int[] A) { 3 if (A.length==0) return 0; 4 if (A.length==1) return 0; 5 int index = 1; 6 int bar = A[0]; 7 int total = 0; 8 int curStore = 0; 9 boolean[] count = new boolean[A.length]; 10 11 //We need to record which column has been counted during the first scan. 12 for (int i=0;i<count.length;i++) count[i] = false; 13 List<Integer> countList = new ArrayList<Integer>(); 14 15 while (index<A.length){ 16 int curBar = A[index]; 17 if (curBar<bar){ 18 curStore+= (bar-curBar); 19 countList.add(index); 20 } else { 21 total += curStore; 22 curStore = 0; 23 bar = curBar; 24 for (int i=0;i<countList.size();i++) count[countList.get(i)]=true; 25 countList.clear(); 26 } 27 index++; 28 } 29 30 bar = A[A.length-1]; 31 index = A.length-2; 32 curStore = 0; 33 while (index>=0){ 34 int curBar = A[index]; 35 if (curBar<bar && !count[index]) 36 curStore+= (bar-curBar); 37 else if (curBar>bar){ 38 total += curStore; 39 curStore = 0; 40 bar = curBar; 41 } 42 index--; 43 } 44 45 46 return total; 47 } 48 }
NOTE: We need to record which column has been counted in the first scan, we then ignor these column in the second scan.
标签：style blog http io color ar os sp for
原文地址：http://www.cnblogs.com/lishiblog/p/4098665.html
