refactor 73

Author: fishercoder1534

src/main/java/com/fishercoder/solutions/_73.java

@@ -131,4 +131,46 @@ public void setZeroes(int[][] matrix) {
             }
         }
     }
+
+    public static class Solution4 {
+        /**
+         * Space: O(1)
+         * credit: https://leetcode.com/problems/set-matrix-zeroes/discuss/26014/Any-shorter-O(1)-space-solution
+         */
+        public void setZeroes(int[][] matrix) {
+            int col0 = 1;
+            int m = matrix.length;
+            int n = matrix[0].length;
+            /**the first iteration (first nested for loop) is to check from top row to bottom row:
+             * keep the first column state into variable col0;
+             * then starting from the second column, check all the rest of the columns and mark its top cell and its most-left cell if it
+             * s a zero.*/
+            for (int i = 0; i < m; i++) {
+                if (matrix[i][0] == 0) {
+                    col0 = 0;
+                }
+
+                for (int j = 1; j < n; j++) {
+                    if (matrix[i][j] == 0) {
+                        matrix[i][0] = 0;
+                        matrix[0][j] = 0;
+                    }
+                }
+            }
+
+            /**the second iteration (second nested for loop) is to check from bottom row to the top row
+             * from the right-most column to the second left-most column: as long as its left-most column cell or its top row cell is zero, then set that cell to be zero
+             * at last, check col0 variable, if it's zero, mark that row cell as zero*/
+            for (int i = m - 1; i >= 0; i--) {
+                for (int j = n - 1; j >= 1; j--) {
+                    if (matrix[i][0] == 0 || matrix[0][j] == 0) {
+                        matrix[i][j] = 0;
+                    }
+                }
+                if (col0 == 0) {
+                    matrix[i][0] = 0;
+                }
+            }
+        }
+    }
 }

src/test/java/com/fishercoder/_73Test.java

@@ -10,6 +10,7 @@ public class _73Test {
     private static _73.Solution1 solution1;
     private static _73.Solution2 solution2;
     private static _73.Solution3 solution3;
+    private static _73.Solution4 solution4;
     private static int[][] matrix;
     private static int[][] expected;
 
@@ -18,6 +19,7 @@ public static void setup() {
         solution1 = new _73.Solution1();
         solution2 = new _73.Solution2();
         solution3 = new _73.Solution3();
+        solution4 = new _73.Solution4();
     }
 
     @Test
@@ -80,4 +82,24 @@ public void test3() {
         assertArrayEquals(expected, matrix);
     }
 
+    @Test
+    public void test4() {
+        matrix = new int[][]{
+                {0, 0, 0, 5},
+                {4, 3, 1, 4},
+                {0, 1, 1, 4},
+                {1, 2, 1, 3},
+                {0, 0, 1, 1}
+        };
+        solution4.setZeroes(matrix);
+        expected = new int[][]{
+                {0, 0, 0, 0},
+                {0, 0, 0, 4},
+                {0, 0, 0, 0},
+                {0, 0, 0, 3},
+                {0, 0, 0, 0}
+        };
+        assertArrayEquals(expected, matrix);
+    }
+
 }