refactor 750

Author: fishercoder1534

README.md

@@ -22,6 +22,7 @@ Your ideas/fixes/algorithms are more than welcome!
 
 |  #  |      Title     |   Solutions   | Time          | Space         | Difficulty  | Tag          | Notes
 |-----|----------------|---------------|---------------|---------------|-------------|--------------|-----
+|750|[Number Of Corner Rectangles](https://leetcode.com/problems/number-of-corner-rectangles/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_750.java) | O((m*n)^2) | O(1) | Medium|
 |748|[Shortest Completing Word](https://leetcode.com/problems/shortest-completing-word/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_748.java) | O(n) | O(1) | Easy|
 |746|[Min Cost Climbing Stairs](https://leetcode.com/problems/min-cost-climbing-stairs/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_746.java) | O(n) | O(1) | Easy|
 |744|[Find Smallest Letter Greater Than Target](https://leetcode.com/problems/find-smallest-letter-greater-than-target/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_744.java) | O(logn) | O(1) | Easy|

src/main/java/com/fishercoder/solutions/_750.java

@@ -0,0 +1,64 @@
+package com.fishercoder.solutions;
+
+/**
+ * 750. Number Of Corner Rectangles
+ *
+ * Given a grid where each entry is only 0 or 1, find the number of corner rectangles.
+ * A corner rectangle is 4 distinct 1s on the grid that form an axis-aligned rectangle.
+ * Note that only the corners need to have the value 1. Also, all four 1s used must be distinct.
+
+ Example 1:
+ Input: grid =
+ [[1, 0, 0, 1, 0],
+ [0, 0, 1, 0, 1],
+ [0, 0, 0, 1, 0],
+ [1, 0, 1, 0, 1]]
+ Output: 1
+ Explanation: There is only one corner rectangle, with corners grid[1][2], grid[1][4], grid[3][2], grid[3][4].
+
+ Example 2:
+ Input: grid =
+ [[1, 1, 1],
+ [1, 1, 1],
+ [1, 1, 1]]
+ Output: 9
+ Explanation: There are four 2x2 rectangles, four 2x3 and 3x2 rectangles, and one 3x3 rectangle.
+
+ Example 3:
+ Input: grid =
+ [[1, 1, 1, 1]]
+ Output: 0
+ Explanation: Rectangles must have four distinct corners.
+
+ Note:
+ The number of rows and columns of grid will each be in the range [1, 200].
+ Each grid[i][j] will be either 0 or 1.
+ The number of 1s in the grid will be at most 6000.*/
+public class _750 {
+  public static class Solution1 {
+    public int countCornerRectangles(int[][] grid) {
+      if (grid == null || grid.length < 2) {
+        return 0;
+      }
+      int m = grid.length;
+      int n = grid[0].length;
+      int count = 0;
+      for (int i = 0; i < m - 1; i++) {
+        for (int j = 0; j < n - 1; j++) {
+          if (grid[i][j] == 1) {
+            for (int jNext = j + 1; jNext < n; jNext++) {
+              if (grid[i][jNext] == 1) {
+                for (int iNext = i + 1; iNext < m; iNext++) {
+                  if (grid[iNext][j] == 1 && grid[iNext][jNext] == 1) {
+                    count++;
+                  }
+                }
+              }
+            }
+          }
+        }
+      }
+      return count;
+    }
+  }
+}

src/test/java/com/fishercoder/_750Test.java

@@ -0,0 +1,43 @@
+package com.fishercoder;
+
+import com.fishercoder.solutions._750;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+
+public class _750Test {
+  private static _750.Solution1 solution1;
+  private static int[][] grid;
+
+  @BeforeClass
+  public static void setup() {
+    solution1 = new _750.Solution1();
+  }
+
+  @Test
+  public void test1() {
+    grid = new int[][] {
+        {1, 0, 0, 1, 0},
+        {0, 0, 1, 0, 1},
+        {0, 0, 0, 1, 0},
+        {1, 0, 1, 0, 1}};
+    assertEquals(1, solution1.countCornerRectangles(grid));
+  }
+
+  @Test
+  public void test2() {
+    grid = new int[][] {
+        {1, 1, 1},
+        {1, 1, 1},
+        {1, 1, 1}};
+    assertEquals(9, solution1.countCornerRectangles(grid));
+  }
+
+  @Test
+  public void test3() {
+    grid = new int[][] {
+        {1, 1, 1, 1}};
+    assertEquals(0, solution1.countCornerRectangles(grid));
+  }
+}