_391.java

package com.fishercoder.solutions;

import java.util.HashSet;
import java.util.Set;

public class _391 {
    public static class Solution1 {
        /**
         * credit: https://discuss.leetcode.com/topic/56052/really-easy-understanding-solution-o-n-java
         */
        public boolean isRectangleCover(int[][] rectangles) {
            if (rectangles.length == 0 || rectangles[0].length == 0) {
                return false;
            }

            int x1 = Integer.MAX_VALUE;
            int x2 = Integer.MIN_VALUE;
            int y1 = Integer.MAX_VALUE;
            int y2 = Integer.MIN_VALUE;

            Set<String> set = new HashSet<>();
            int area = 0;

            for (int[] rect : rectangles) {
                x1 = Math.min(rect[0], x1);
                y1 = Math.min(rect[1], y1);
                x2 = Math.max(rect[2], x2);
                y2 = Math.max(rect[3], y2);

                area += (rect[2] - rect[0]) * (rect[3] - rect[1]);

                String s1 = rect[0] + " " + rect[1];
                String s2 = rect[0] + " " + rect[3];
                String s3 = rect[2] + " " + rect[3];
                String s4 = rect[2] + " " + rect[1];

                if (!set.add(s1)) {
                    set.remove(s1);
                }
                if (!set.add(s2)) {
                    set.remove(s2);
                }
                if (!set.add(s3)) {
                    set.remove(s3);
                }
                if (!set.add(s4)) {
                    set.remove(s4);
                }
            }

            if (!set.contains(x1 + " " + y1) || !set.contains(x1 + " " + y2) || !set.contains(
                    x2 + " " + y1) || !set.contains(x2 + " " + y2) || set.size() != 4) {
                return false;
            }

            return area == (x2 - x1) * (y2 - y1);
        }
    }
}