391. Perfect Rectangle

391. Perfect Rectangle

Given N axis-aligned rectangles where N > 0, determine if they all together form an exact cover of a rectangular region.

Each rectangle is represented as a bottom-left point and a top-right point. For example, a unit square is represented as [1,1,2,2]. (coordinate of bottom-left point is (1, 1) and top-right point is (2, 2)).

Example 1:

rectangles = [ [1,1,3,3], [3,1,4,2], [3,2,4,4], [1,3,2,4], [2,3,3,4]]Return true. All 5 rectangles together form an exact cover of a

Example 2:

rectangles = [ [1,1,2,3], [1,3,2,4], [3,1,4,2], [3,2,4,4]]Return false. Because there is a gap between the two

Example 3:

rectangles = [ [1,1,3,3], [3,1,4,2], [1,3,2,4], [3,2,4,4]]Return false. Because there is a gap in the

Example 4:

rectangles = [ [1,1,3,3], [3,1,4,2], [1,3,2,4], [2,2,4,4]]Return false. Because two of the rectangles overlap with each

思路： 能够正好围成一个矩形的情况有且只有: 1、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) 2、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)

class Solution { public boolean isRectangleCover(int[][] rectangles) { int left = Integer.MAX_VALUE; int right = Integer.MIN_VALUE; int top = Integer.MIN_VALUE; int bottom = Integer.MAX_VALUE; int n = rectangles.length; HashSet flags = new HashSet(); int totalArea = 0; for(int i=0;i

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