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Last Updated: 25 Jan, 2022

Set Matrix Zeros

Easy
Asked in companies
GoogleAmazonDunzo

Problem statement

Given an ‘N’ x ‘M’ integer matrix, if an element is 0, set its entire row and column to 0's, and return the matrix. In particular, your task is to modify it in such a way that if a cell has a value 0 (matrix[i][j] == 0), then all the cells of the ith row and jth column should be changed to 0.

You must do it in place.

For Example:

If the given grid is this:
[7, 19, 3]
[4, 21, 0]

Then the modified grid will be:
[7, 19, 0]
[0, 0,  0]

Input Format:

The first line of the input contains a single integer ‘T’ representing the no. of test cases.

The first line of each test case contains two space-separated integers ‘N’ and ‘M’, denoting the no. of the rows and columns of the matrix.

The next 'N' lines will contain ‘M’ space separated integers representing the elements of the matrix.

Output Format:

For each test case, print the modified grid.

Print output of each test case in a separate line.

Note:

You are not required to print anything; it has already been taken care of. Just implement the function and return the answer.

Constraints:

1 ≤ T ≤ 1000
1 ≤ m, n ≤ 1000
Σ(m * n) ≤ 2000000
-2^(31) ≤ matrix[i][j] ≤ 2^(31)-1, for all (1 ≤ i ≤ n and 1 ≤ j ≤ m).

Time Limit: 1 sec

Follow up:

Can we do better than O(m * n) space?
Using O(m + n) space is an improvement but we can still do better.
We can do it using constant memory. Can you do it?

Approaches

01 Approach

The basic idea is to maintain another boolean matrix ‘isZero’ which stores whether our resultant matrix should contain a zero at a particular index or not. We can traverse every element of our original matrix. If the element is 0, then we traverse the complete row and complete column of that particular element and set isZero values accordingly to true for all the elements in that row and column.

 

Algorithm: 

 

setZeros(matrix)

  • Store dimensions of the matrix in n and m
  • Declare “isZero” boolean matrix of size n x m.
  • Iterate over i from 0 to n
    • Iterate over j from 0 to m
      • If matrix[i][j] == 0
        • Iterate over k from 0 to n
          • Set isZero[k][j] = true
        • Iterate over k from 0 to m
          • Set isZero[i][k] = true
  • Iterate over i from 0 to n
    • Iterate over j from 0 to m
      • If isZero[i][j] == true
        • Set matrix[i][j] = 0