refactor: 73. Set Matrix Zeroes to reduce Space complexity to O(1)

Author: gwbaik9717

set-matrix-zeroes/gwbaik9717.js

@@ -1,6 +1,6 @@
 // m: height of matrix, n: width of matrix
 // Time complexity: O(m*n)
-// Space complexity: O(m+n)
+// Space complexity: O(1)
 
 /**
  * @param {number[][]} matrix
@@ -10,27 +10,60 @@ var setZeroes = function (matrix) {
   const h = matrix.length;
   const w = matrix[0].length;
 
-  const setY = new Set();
-  const setX = new Set();
+  // a flag for iterating rows of the first column
+  let temp1 = false;
+
+  // a flag for iterating cols of the first row
+  let temp2 = false;
 
   for (let i = 0; i < h; i++) {
-    for (let j = 0; j < w; j++) {
+    if (matrix[i][0] === 0) {
+      temp1 = true;
+      break;
+    }
+  }
+
+  for (let i = 0; i < w; i++) {
+    if (matrix[0][i] === 0) {
+      temp2 = true;
+      break;
+    }
+  }
+
+  for (let i = 1; i < h; i++) {
+    for (let j = 1; j < w; j++) {
       if (matrix[i][j] === 0) {
-        setY.add(i);
-        setX.add(j);
+        matrix[i][0] = 0;
+        matrix[0][j] = 0;
       }
     }
   }
 
-  for (const y of setY) {
-    for (let x = 0; x < w; x++) {
-      matrix[y][x] = 0;
+  for (let i = 1; i < h; i++) {
+    if (matrix[i][0] === 0) {
+      for (let j = 1; j < w; j++) {
+        matrix[i][j] = 0;
+      }
     }
   }
 
-  for (const x of setX) {
-    for (let y = 0; y < h; y++) {
-      matrix[y][x] = 0;
+  for (let i = 1; i < w; i++) {
+    if (matrix[0][i] === 0) {
+      for (let j = 1; j < h; j++) {
+        matrix[j][i] = 0;
+      }
+    }
+  }
+
+  if (temp1) {
+    for (let i = 0; i < h; i++) {
+      matrix[i][0] = 0;
+    }
+  }
+
+  if (temp2) {
+    for (let j = 0; j < w; j++) {
+      matrix[0][j] = 0;
     }
   }
 };