solve problem

leet-code/73-set-matrix-zeroes/README.md

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+# 73-set-matrix-zeroes
+
+Given an m x n integer matrix matrix, if an element is 0, set its entire row and column to 0's.
+
+Input: matrix = [[1,1,1],[1,0,1],[1,1,1]]
+Output: [[1,0,1],[0,0,0],[1,0,1]]
+
+
+Input: matrix = [[0,1,2,0],[3,4,5,2],[1,3,1,5]]
+Output: [[0,0,0,0],[0,4,5,0],[0,3,1,0]]
+
+Constraints:
+
+m == matrix.length
+n == matrix[0].length
+1 <= m, n <= 200
+-231 <= matrix[i][j] <= 231 - 1
+
+
+Follow up:
+
+A straightforward solution using O(mn) space is probably a bad idea.
+A simple improvement uses O(m + n) space, but still not the best solution.
+Could you devise a constant space solution?

leet-code/73-set-matrix-zeroes/index.js

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+/**
+ * @param {number[][]} matrix
+ * @return {void} Do not return anything, modify matrix in-place instead.
+ */
+var setZeroes = function(matrix) {
+    // store which rows and columns need to be zero-ed out
+    const flags = {}
+    // find the existing zeros 
+    for(let i = 0; i < matrix.length; i++) {
+        for (let j = 0; j < matrix[i].length; j++) {
+            if (matrix[i][j] !== 0) continue;
+            // mark row and column to be mutated
+            flags[`r${i}`] = true;
+            flags[`c${j}`] = true;
+        }
+    }
+    // mutate the matrix
+    for(let i = 0; i < matrix.length; i++) {
+        for (let j = 0; j < matrix[i].length; j++) {
+            if (flags[`r${i}`] || flags[`c${j}`]) matrix[i][j] = 0 
+        }
+    }
+
+    return matrix;
+};