1 import java.util.HashSet;
 2
 3 /** * 核心思想就是:能够正好围成一个矩形的情况就是:
 4  * 有且只有:
 5  * - 最左下 最左上 最右下 最右上 的四个点只出现过一次,其他肯定是成对出现的(保证完全覆盖)
 6  * - 上面四个点围成的面积,正好等于所有子矩形的面积之和(保证不重复)
 7  * Created by MebiuW on 16/8/29. */
 8
 9 public class Solution{
10     public boolean isRectangleCover(int[][] rectangles){
11         int left=Integer.MAX_VALUE;
12         int right=Integer.MIN_VALUE;
13         int top=Integer.MIN_VALUE;
14         int bottom=Integer.MAX_VALUE;
15         int n=rectangles.length;
16         HashSet<String> flags=new HashSet<String>();
17         int totalArea=0;
18         for(int i=0;i<n;i++){
19             left=Math.min(left,rectangles[i][0]);
20             bottom=Math.min(bottom,rectangles[i][1]);
21             right=Math.max(right,rectangles[i][2]);
22             top=Math.max(top,rectangles[i][3]);
23             totalArea+=(rectangles[i][3]-rectangles[i][1])*(rectangles[i][2]-rectangles[i][0]);
24             String pointLT=rectangles[i][0]+" "+rectangles[i][3];
25             String pointLB=rectangles[i][0]+" "+rectangles[i][1];
26             String pointRT=rectangles[i][2]+" "+rectangles[i][3];
27             String pointRB=rectangles[i][2]+" "+rectangles[i][1];
28             if(!flags.contains(pointLT)) flags.add(pointLT);
29             else flags.remove(pointLT);
30             if(!flags.contains(pointLB)) flags.add(pointLB);
31             else flags.remove(pointLB);
32             if(!flags.remove(pointRT)) flags.add(pointRT);
33             else flags.remove(pointRT);
34             if(!flags.contains(pointRB)) flags.add(pointRB);
35             else flags.remove(pointRB);
36         }
37         if(flags.size()==4&&flags.contains(left+" "+top)
38                 &&flags.contains(left+" "+bottom)
39                 &&flags.contains(right+" "+bottom)
40                 &&flags.contains(right+" "+top)){
41             return totalArea==(right-left)*(top-bottom);
42         }
43         return false;
44     }
45 }