Merge pull request #16151 from anujgaud/ag/set-matrix-to-zeroes

Ag/set matrix to zeroes

core-java-modules/core-java-arrays-operations-advanced-2/src/main/java/com/baeldung/matrixtozero/SetMatrixToZero.java

@@ -0,0 +1,147 @@
+package com.baeldung.matrixtozero;
+
+import java.util.*;
+
+public class SetMatrixToZero{
+    static void setZeroesByNaiveApproach(int[][] matrix) {
+        int row = matrix.length;
+        int col = matrix[0].length;
+        int [][] result = new int[row][col];
+
+        for(int i = 0; i<row; i++){
+            for(int j = 0; j < col; j++){
+                result[i][j] = matrix[i][j];
+            }
+        }
+        
+        for(int i = 0; i < row; i++){
+            for(int j = 0; j < col; j++){
+                if(matrix[i][j] == 0){
+                    for(int k = 0; k < col; k++){
+                        result[i][k] = 0;
+                    }
+                    for(int k = 0; k < row; k++){
+                        result[k][j] = 0;
+                    }
+                }
+            }
+        }
+
+        for(int i = 0; i < row; i++){
+            for(int j = 0; j < col; j++){
+                matrix[i][j] = result[i][j];
+            }
+        }
+    }
+    
+    static void setZeroesByTimeOptimizedApproach(int[][] matrix) {
+        int rows = matrix.length;
+        int cols = matrix[0].length;
+
+        Set<Integer> rowSet = new HashSet<>();
+        Set<Integer> colSet = new HashSet<>();
+
+        for(int i = 0; i < rows; i++){
+            for(int j = 0; j < cols; j++){
+                if (matrix[i][j] == 0){
+                    rowSet.add(i);
+                    colSet.add(j);
+                }
+            }
+        }
+        
+        for(int row: rowSet){
+            for(int j = 0; j < cols; j++){
+                matrix[row][j] = 0;
+            }
+        }
+        
+        for(int col: colSet) {
+            for(int i = 0; i < rows; i++){
+                matrix[i][col] = 0;
+            }
+        }
+    } 
+
+    static boolean hasZeroInFirstRow(int[][] matrix, int cols) {
+        for (int j = 0; j < cols; j++) {
+            if (matrix[0][j] == 0) {
+                return true;
+            }
+        }
+        return false;
+    }
+
+    static boolean hasZeroInFirstCol(int[][] matrix, int rows) {
+        for (int i = 0; i < rows; i++) {
+            if (matrix[i][0] == 0) {
+                return true;
+            }
+        }
+        return false;
+    }
+
+    static void markZeroesInMatrix(int[][] matrix, int rows, int cols) {
+        for (int i = 1; i < rows; i++) {
+            for (int j = 1; j < cols; j++) {
+                if (matrix[i][j] == 0) {
+                    matrix[i][0] = 0;
+                    matrix[0][j] = 0;
+                }
+            }
+        }
+    }
+
+    static void setZeroesInRows(int[][] matrix, int rows, int cols) {
+        for (int i = 1; i < rows; i++) {
+            if (matrix[i][0] == 0) {
+                for (int j = 1; j < cols; j++) {
+                    matrix[i][j] = 0;
+                }
+            }
+        }
+    }
+
+    static void setZeroesInCols(int[][] matrix, int rows, int cols) {
+        for (int j = 1; j < cols; j++) {
+            if (matrix[0][j] == 0) {
+                for (int i = 1; i < rows; i++) {
+                    matrix[i][j] = 0;
+                }
+            }
+        }
+    }
+
+    static void setZeroesInFirstRow(int[][] matrix, int cols) {
+        for (int j = 0; j < cols; j++) {
+            matrix[0][j] = 0;
+        }
+    }
+
+    static void setZeroesInFirstCol(int[][] matrix, int rows) {
+        for (int i = 0; i < rows; i++) {
+            matrix[i][0] = 0;
+        }
+    }
+
+    static void setZeroesByOptimalApproach(int[][] matrix) {
+        int rows = matrix.length;
+        int cols = matrix[0].length;
+        
+        boolean firstRowZero = hasZeroInFirstRow(matrix, cols);
+        boolean firstColZero = hasZeroInFirstCol(matrix, rows);
+        
+        markZeroesInMatrix(matrix, rows, cols);
+        
+        setZeroesInRows(matrix, rows, cols);
+        setZeroesInCols(matrix, rows, cols);
+        
+        if (firstRowZero) {
+            setZeroesInFirstRow(matrix, cols);
+        }
+        if (firstColZero) {
+            setZeroesInFirstCol(matrix, rows);
+        }
+    }
+
+}

core-java-modules/core-java-arrays-operations-advanced-2/src/test/java/com/baeldung/matrixtozero/SetMatrixToZeroUnitTest.java

@@ -0,0 +1,54 @@
+package com.baeldung.matrixtozero;
+
+import static org.junit.jupiter.api.Assertions.assertArrayEquals;
+import org.junit.jupiter.api.Test;
+
+public class SetMatrixToZeroUnitTest{
+    @Test 
+    void givenMatrix_whenUsingSetZeroesByNaiveApproach_thenSetZeroes() {
+        int[][] matrix = {
+                {1, 2, 3},
+                {4, 0, 6},
+                {7, 8, 9}
+        };
+        int[][] expected = {
+                {1, 0, 3},
+                {0, 0, 0},
+                {7, 0, 9}
+        };
+        SetMatrixToZero.setZeroesByNaiveApproach(matrix);
+        assertArrayEquals(expected, matrix);
+    }
+
+    @Test
+    void givenMatrix_whenUsingSetZeroesByTimeOptimizedApproach_thenSetZeroes() {
+        int[][] matrix = {
+                {1, 2, 3},
+                {4, 0, 6},
+                {7, 8, 9}
+        };
+        int[][] expected = {
+                {1, 0, 3},
+                {0, 0, 0},
+                {7, 0, 9}
+        };
+        SetMatrixToZero.setZeroesByTimeOptimizedApproach(matrix);
+        assertArrayEquals(expected, matrix);
+    }
+
+    @Test
+    void givenMatrix_whenUsingSetZeroesByOptimalApproach_thenSetZeroes() {
+        int[][] matrix = {
+                {1, 2, 3},
+                {4, 0, 6},
+                {7, 8, 9}
+        };
+        int[][] expected = {
+                {1, 0, 3},
+                {0, 0, 0},
+                {7, 0, 9}
+        };
+        SetMatrixToZero.setZeroesByOptimalApproach(matrix);
+        assertArrayEquals(expected, matrix);
+    }
+}