题目：

题解：

class Solution {public boolean isRectangleCover(int[][] rectangles) {long area = 0;int minX = rectangles[0][0], minY = rectangles[0][1], maxX = rectangles[0][2], maxY = rectangles[0][3];Map<Point, Integer> cnt = new HashMap<Point, Integer>();for (int[] rect : rectangles) {int x = rect[0], y = rect[1], a = rect[2], b = rect[3];area += (long) (a - x) * (b - y);minX = Math.min(minX, x);minY = Math.min(minY, y);maxX = Math.max(maxX, a);maxY = Math.max(maxY, b);Point point1 = new Point(x, y);Point point2 = new Point(x, b);Point point3 = new Point(a, y);Point point4 = new Point(a, b);cnt.put(point1, cnt.getOrDefault(point1, 0) + 1);cnt.put(point2, cnt.getOrDefault(point2, 0) + 1);cnt.put(point3, cnt.getOrDefault(point3, 0) + 1);cnt.put(point4, cnt.getOrDefault(point4, 0) + 1);}Point pointMinMin = new Point(minX, minY);Point pointMinMax = new Point(minX, maxY);Point pointMaxMin = new Point(maxX, minY);Point pointMaxMax = new Point(maxX, maxY);if (area != (long) (maxX - minX) * (maxY - minY) || cnt.getOrDefault(pointMinMin, 0) != 1 || cnt.getOrDefault(pointMinMax, 0) != 1 || cnt.getOrDefault(pointMaxMin, 0) != 1 || cnt.getOrDefault(pointMaxMax, 0) != 1) {return false;}cnt.remove(pointMinMin);cnt.remove(pointMinMax);cnt.remove(pointMaxMin);cnt.remove(pointMaxMax);for (Map.Entry<Point, Integer> entry : cnt.entrySet()) {int value = entry.getValue();if (value != 2 && value != 4) {return false;}}return true;}
}class Point {int x;int y;public Point(int x, int y) {this.x = x;this.y = y;}@Overridepublic int hashCode() {return x + y;}@Overridepublic boolean equals(Object obj) {if (obj instanceof Point) {Point point2 = (Point) obj;return this.x == point2.x && this.y == point2.y;}return false;}
}