avc278 - 1.08 - Javascript (#63)

Added my solution to the Chapter 1 Problem 8 folder.

Author: avc278

JavaScript/chapter01/p08_zero_matrix/avc278.js

@@ -0,0 +1,96 @@
+// Zero Matrix: Write an algorithm such that if an element in an MxN matrix is 0, its entire row and columns are set to 0.
+
+const assert = require("assert");
+
+/**
+ * Overwrite rows and columns who have at least 1 zero in them with zeros.
+ * @param  {Array.<number[]>} matrix input 2d array to mutate
+ * @return {null}
+ *
+ * We start by initializing rows and cols arrays with false values. We iterate through the matrix, and when we find a 0,
+ * we flag its row and column by updating the corresponding indices in rows and cols for future use.
+ * When we take a second pass at the matrix, we update all rows that have been flagged to 0, and all columns that have
+ * been flagged to 0, which is O(M + N).
+ *
+ * Runtime: O(M * N)
+ * Space:   O(M + N)
+ *
+ */
+const zeroMatrix = (arr) => {
+  if (arr.length === 0 || arr[0].length === 0) return;
+  const rows = new Array(arr.length).fill(false);
+  const cols = new Array(arr[0].length).fill(false);
+
+  for (let i = 0; i < arr.length; i++) {
+    for (let j = 0; j < arr[0].length; j++) {
+      if (arr[i][j] !== 0) continue;
+      rows[i] = true;
+      cols[j] = true;
+    }
+  }
+
+  for (let i = 0; i < arr.length; i++) {
+    if (!rows[i]) continue;
+    for (let j = 0; j < arr[0].length; j++) {
+      arr[i][j] = 0;
+    }
+  }
+
+  for (let j = 0; j < arr[0].length; j++) {
+    if (!cols[j]) continue;
+    for (let i = 0; i < arr.length; i++) {
+      arr[i][j] = 0;
+    }
+  }
+};
+
+describe(module.filename, () => {
+  it("should not affect a matrix of size 0", () => {
+    const matrix = [];
+
+    zeroMatrix(matrix);
+    assert.deepEqual(matrix, []);
+  });
+  it("should not affect a matrix without 0s", () => {
+    const matrix = [
+      [1, 2, 3],
+      [4, 5, 6],
+      [7, 8, 9],
+    ];
+
+    zeroMatrix(matrix);
+    assert.deepEqual(matrix, [
+      [1, 2, 3],
+      [4, 5, 6],
+      [7, 8, 9],
+    ]);
+  });
+  it("should update all rows and columns with at least one 0 to all 0s", () => {
+    const matrix = [
+      [0, 2, 3, 1],
+      [4, 5, 6, 1],
+      [7, 8, 9, 1],
+    ];
+
+    zeroMatrix(matrix);
+    assert.deepEqual(matrix, [
+      [0, 0, 0, 0],
+      [0, 5, 6, 1],
+      [0, 8, 9, 1],
+    ]);
+  });
+  it("should update all rows and columns with at least one 0 to all 0s when multiple 0s are present", () => {
+    const matrix = [
+      [0, 2, 3],
+      [4, 5, 0],
+      [7, 8, 9],
+    ];
+
+    zeroMatrix(matrix);
+    assert.deepEqual(matrix, [
+      [0, 0, 0],
+      [0, 0, 0],
+      [0, 8, 0],
+    ]);
+  });
+});