Add Zero Striping

Author: marttp

kotlin/Hash Maps and Sets/ZeroStriping.kt

@@ -0,0 +1,57 @@
+fun zeroStriping(matrix: MutableList<MutableList<Int>>) {
+    if (matrix.isEmpty() || matrix[0].isEmpty()) {
+        return
+    }
+    val m = matrix.size
+    val n = matrix[0].size
+    // Check if the first row initially contains a zero.
+    var firstRowHasZero = false
+    for (c in 0 until n) {
+        if (matrix[0][c] == 0) {
+            firstRowHasZero = true
+            break
+        }
+    }
+    // Check if the first column initially contains a zero.
+    var firstColHasZero = false
+    for (r in 0 until m) {
+        if (matrix[r][0] == 0) {
+            firstColHasZero = true
+            break
+        }
+    }
+    // Use the first row and column as markers. If an element in the 
+    // submatrix is zero, mark its corresponding row and column in the 
+    // first row and column as 0.
+    for (r in 1 until m) {
+        for (c in 1 until n) {
+            if (matrix[r][c] == 0) {
+                matrix[0][c] = 0
+                matrix[r][0] = 0
+            }
+        }
+    }
+    // Update the submatrix using the markers in the first row and 
+    // column.
+    for (r in 1 until m) {
+        for (c in 1 until n) {
+            if (matrix[0][c] == 0 || matrix[r][0] == 0) {
+                matrix[r][c] = 0
+            }
+        }
+    }
+    // If the first row had a zero initially, set all elements in the 
+    // first row to zero.
+    if (firstRowHasZero) {
+        for (c in 0 until n) {
+            matrix[0][c] = 0
+        }
+    }
+    // If the first column had a zero initially, set all elements in 
+    // the first column to zero.
+    if (firstColHasZero) {
+        for (r in 0 until m) {
+            matrix[r][0] = 0
+        }
+    }
+}

kotlin/Hash Maps and Sets/ZeroStripingHashSets.kt

@@ -0,0 +1,29 @@
+fun zeroStripingHashSets(matrix: MutableList<MutableList<Int>>) {
+    if (matrix.isEmpty() || matrix[0].isEmpty()) {
+        return
+    }
+    val m = matrix.size
+    val n = matrix[0].size
+    val zeroRows = hashSetOf<Int>()
+    val zeroCols = hashSetOf<Int>()
+    // Pass 1: Traverse through the matrix to identify the rows and
+    // columns containing zeros and store their indexes in the 
+    // appropriate hash sets.
+    for (r in 0 until m) {
+        for (c in 0 until n) {
+            if (matrix[r][c] == 0) {
+                zeroRows.add(r)
+                zeroCols.add(c)
+            }
+        }
+    }
+    // Pass 2: Set any cell in the matrix to zero if its row index is 
+    // in 'zero_rows' or its column index is in 'zero_cols'.
+    for (r in 0 until m) {
+        for (c in 0 until n) {
+            if (r in zeroRows || c in zeroCols) {
+                matrix[r][c] = 0
+            }
+        }
+    }
+}