ZeroMatrix done

Author: rampatra

src/main/java/com/ctci/arraysandstrings/RotateMatrix.java

@@ -0,0 +1,16 @@
+package com.ctci.arraysandstrings;
+
+/**
+ * @author rampatra
+ * @since 2019-01-20
+ */
+public class RotateMatrix {
+
+    public static void rotateImage(int[][] pixels) {
+        
+    }
+
+    public static void main(String[] args) {
+        
+    }
+}

src/main/java/com/ctci/arraysandstrings/StringCompression.java

@@ -31,6 +31,7 @@ private static String compressString(String str) {
 
     public static void main(String[] args) {
         System.out.println("aabccccaaa: " + compressString("aabccccaaa"));
+        System.out.println("aabccccAAAA: " + compressString("aabccccAAAA"));
         System.out.println("abcd: " + compressString("abcd"));
         System.out.println("a: " + compressString("a"));
         System.out.println("aabcccccccccccccccccccccccccaaa: " + compressString("aabcccccccccccccccccccccccccaaa"));

src/main/java/com/ctci/arraysandstrings/ZeroMatrix.java

@@ -0,0 +1,78 @@
+package com.ctci.arraysandstrings;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * Write an algorithm such that if an element in an MxN matrix is 0, its entire row
+ * and column are set to 0.
+ *
+ * @author rampatra
+ * @since 2019-01-20
+ */
+public class ZeroMatrix {
+
+    private static void zeroMatrix(int[][] matrix) {
+        // keep count of which rows and columns have a number zero
+        List<Integer> rowsToZero = new ArrayList<>();
+        List<Integer> colsToZero = new ArrayList<>();
+
+        for (int i = 0; i < matrix.length; i++) {
+            for (int j = 0; j < matrix[0].length; j++) {
+                if (matrix[i][j] == 0) {
+                    rowsToZero.add(i);
+                    colsToZero.add(j);
+                }
+            }
+        }
+
+        makeRowColumnZero(matrix, rowsToZero, colsToZero);
+    }
+
+    private static void makeRowColumnZero(int[][] matrix, List<Integer> rows, List<Integer> cols) {
+        for (int row : rows) {
+            // make entire row zero
+            for (int c = 0; c < matrix[0].length; c++) {
+                matrix[row][c] = 0;
+            }
+        }
+        for (int col : cols) {
+            // make entire column zero
+            for (int r = 0; r < matrix.length; r++) {
+                matrix[r][col] = 0;
+            }
+        }
+    }
+
+    private static void printMatrix(int[][] matrix) {
+        for (int i = 0; i < matrix.length; i++) {
+            for (int j = 0; j < matrix[0].length; j++) {
+                System.out.print(matrix[i][j]);
+                if (j + 1 >= matrix[0].length) {
+                    System.out.println();
+                }
+            }
+        }
+    }
+
+    public static void main(String[] args) {
+        int[][] m = new int[][]{{0, 1, 2}, {3, 4, 5}, {6, 7, 8}};
+        printMatrix(m);
+        zeroMatrix(m);
+        System.out.println("---");
+        printMatrix(m);
+        System.out.println("---");
+        m = new int[][]{{1, 0, 2}, {3, 4, 5}, {6, 7, 8}};
+        printMatrix(m);
+        zeroMatrix(m);
+        System.out.println("---");
+        printMatrix(m);
+        System.out.println("---");
+        m = new int[][]{{1, 2, 0}, {3, 4, 5}, {6, 7, 8}};
+        printMatrix(m);
+        zeroMatrix(m);
+        System.out.println("---");
+        printMatrix(m);
+        System.out.println("---");
+    }
+}