Set Matrix Zeroes In Place in DSA Go - Build from Scratch

Set Matrix Zeroes In Place

📖 Scenario: You are working on a spreadsheet application. Sometimes, when a cell in the spreadsheet is zero, the entire row and column of that cell should be cleared (set to zero) to indicate invalid or missing data.We want to update the spreadsheet matrix directly without using extra space for another matrix.

🎯 Goal: Write a Go program that modifies a 2D matrix in place. If any cell is zero, set its entire row and column to zero.

📋 What You'll Learn

Create a 2D slice of integers called matrix with the exact values [[1,1,1],[1,0,1],[1,1,1]]

Create two boolean variables firstRowHasZero and firstColHasZero to track zeros in the first row and first column

Implement the logic to set rows and columns to zero in place using the first row and column as markers

Print the modified matrix after applying the zeroing logic

💡 Why This Matters

🌍 Real World

Spreadsheet software and data cleaning tools often need to clear rows and columns based on invalid or missing data.

💼 Career

Understanding in-place matrix manipulation is useful for software engineers working with image processing, data analysis, and performance-critical applications.

1

Create the initial matrix

Create a 2D slice of integers called matrix with these exact values: [[1,1,1],[1,0,1],[1,1,1]]

DSA Go

# Create the matrix variable with the given values
# Your code here

Hint

Use a slice of slices to create the 2D matrix with the exact rows and columns.

2

Add variables to track zeros in first row and column

Create two boolean variables called firstRowHasZero and firstColHasZero and set them to false initially

DSA Go

package main

import "fmt"

func main() {
    matrix := [][]int{
        {1, 1, 1},
        {1, 0, 1},
        {1, 1, 1},
    }
    // Create two boolean variables to track zeros in first row and first column
    // Your code here
}

Hint

Use varName := false to create boolean variables.

3

Implement the in-place zeroing logic

Write the code inside main to: 1. Check if the first row has any zero and update firstRowHasZero 2. Check if the first column has any zero and update firstColHasZero 3. Use the first row and column to mark zeros for other rows and columns 4. Set zeros in the matrix based on these markers 5. Finally, set zeros in the first row and first column if needed

DSA Go

package main

import "fmt"

func main() {
    matrix := [][]int{
        {1, 1, 1},
        {1, 0, 1},
        {1, 1, 1},
    }
    firstRowHasZero := false
    firstColHasZero := false

    // Your code here to implement the zeroing logic
}

Hint

Use nested loops and the first row and column as markers to track zeros. Then update the matrix accordingly.

4

Print the modified matrix

Write a for loop to print each row of the matrix after modification using fmt.Println(matrix[i])

DSA Go

package main

import "fmt"

func main() {
    matrix := [][]int{
        {1, 1, 1},
        {1, 0, 1},
        {1, 1, 1},
    }
    firstRowHasZero := false
    firstColHasZero := false

    // ... previous logic ...

    // Print each row of the matrix
    // Your code here

Hint

Use a for loop from 0 to len(matrix) and print each row with fmt.Println(matrix[i]).

Practice

1. What is the main goal of the Set Matrix Zeroes In Place problem?

easy

A. Modify the matrix so that if an element is 0, its entire row and column become 0

B. Find the sum of all elements in the matrix

C. Sort each row of the matrix in ascending order

D. Transpose the matrix without changing its elements

Solution

1. Step 1: Understand the problem requirement

   The problem asks to change the matrix so that any row or column containing a zero should be set entirely to zero.

2. Step 2: Identify the correct operation

   Only Modify the matrix so that if an element is 0, its entire row and column become 0 describes this exact operation, modifying rows and columns based on zero elements.

3. Final Answer:

   Modify the matrix so that if an element is 0, its entire row and column become 0 -> Option A

4. Quick Check:

   Set rows and columns to zero = Modify matrix [OK]

Hint: Remember: zero means zero out whole row and column [OK]

Common Mistakes:

• Confusing with matrix transpose
• Trying to sum elements instead of modifying
• Sorting rows instead of zeroing

2. Which of the following Go code snippets correctly declares a fixed-size 2D array of integers?

easy

A. matrix := [][]int{{1, 2}, {3, 4}}

B. matrix := [2][2]int{{1, 2}, {3, 4}}

C. matrix := [][]int{1, 2, 3, 4}

D. matrix := [2]int{1, 2, 3, 4}

Solution

1. Step 1: Understand Go 2D array declaration

   In Go, fixed-size 2D arrays use syntax like [rows][cols]type, so [2][2]int is a 2x2 matrix.

2. Step 2: Check each option

   matrix := [2][2]int{{1, 2}, {3, 4}} correctly declares a 2x2 integer array with values. matrix := [][]int{{1, 2}, {3, 4}} is a slice of slices (dynamic), not a fixed-size array. matrix := [][]int{1, 2, 3, 4} and D are invalid for 2D matrix.

3. Final Answer:

   matrix := [2][2]int{{1, 2}, {3, 4}} -> Option B

4. Quick Check:

   Fixed 2D array syntax = [2][2]int [OK]

Hint: Use [rows][cols]type for fixed 2D arrays in Go [OK]

Common Mistakes:

• Using slice syntax when fixed array needed
• Incorrect nesting of braces
• Declaring 1D array instead of 2D

3. What will be the matrix after running the following Go code snippet?

matrix := [][]int{
  {1, 2, 3},
  {4, 0, 6},
  {7, 8, 9},
}
// After applying Set Matrix Zeroes In Place logic
// (zero out rows and columns containing zero)

medium

A. [[1, 0, 3], [0, 0, 0], [0, 0, 0]]

B. [[1, 2, 3], [0, 0, 0], [7, 0, 9]]

C. [[1, 0, 3], [0, 0, 0], [7, 0, 9]]

D. [[0, 0, 0], [0, 0, 0], [0, 0, 0]]

Solution

1. Step 1: Identify zero positions

   Zero is at matrix[1][1]. So row 1 and column 1 must be zeroed.

2. Step 2: Apply zeroing

   Row 1 becomes [0,0,0]. Column 1 elements at rows 0 and 2 become 0. So matrix[0][1] and matrix[2][1] are zero.

3. Final Answer:

   [[1, 0, 3], [0, 0, 0], [7, 0, 9]] -> Option C

4. Quick Check:

   Zero row and column applied correctly = [[1,0,3],[0,0,0],[7,0,9]] [OK]

Hint: Zero entire row and column for each zero found [OK]

Common Mistakes:

• Zeroing entire matrix
• Missing zero in column 1 for rows 0 and 2
• Zeroing wrong rows or columns

4. Consider this Go function snippet for setting matrix zeroes:

func setZeroes(matrix [][]int) {
  for i := 0; i < len(matrix); i++ {
    for j := 0; j < len(matrix[0]); j++ {
      if matrix[i][j] == 0 {
        for k := 0; k < len(matrix); k++ {
          matrix[k][j] = 0
        }
        for l := 0; l < len(matrix[0]); l++ {
          matrix[i][l] = 0
        }
      }
    }
  }
}

What is the main problem with this code?

medium

A. It only zeros rows but not columns

B. It uses wrong loop ranges for rows and columns

C. It does not check for zero elements at all

D. It modifies the matrix while iterating, causing incorrect zeroing

Solution

1. Step 1: Analyze matrix modification during iteration

   The code sets zeros immediately when it finds a zero, changing matrix elements during iteration.

2. Step 2: Understand side effects

   This causes new zeros to appear and triggers more zeroing incorrectly, leading to wrong final matrix.

3. Final Answer:

   It modifies the matrix while iterating, causing incorrect zeroing -> Option D

4. Quick Check:

   In-place modification during scan = incorrect zeroing [OK]

Hint: Mark zeros first, then update matrix to avoid side effects [OK]

Common Mistakes:

• Changing matrix while scanning
• Not using extra storage or flags
• Assuming immediate zeroing is safe

5. You want to set matrix zeroes in place with O(1) extra space. Which approach below correctly achieves this in Go?

hard

A. Use first row and first column as markers to track zero rows and columns, then update matrix accordingly

B. Create a separate boolean matrix to mark zero rows and columns, then update original matrix

C. Copy matrix to a new matrix and update zeros there to avoid modifying original during iteration

D. Use recursion to zero rows and columns when zero found

Solution

1. Step 1: Understand space constraints

   O(1) extra space means no additional matrix or large data structures allowed.

2. Step 2: Use first row and column as markers

   Mark zeros in first row and column to remember which rows and columns to zero later, then update matrix in place.

3. Step 3: Avoid extra space and recursion

   Options A and B use extra space, D uses recursion unnecessarily.

4. Final Answer:

   Use first row and first column as markers to track zero rows and columns, then update matrix accordingly -> Option A

5. Quick Check:

   In-place markers = O(1) space zeroing [OK]

Hint: Use matrix edges as flags to save space [OK]

Common Mistakes:

• Using extra arrays violating space constraint
• Modifying matrix during iteration without markers
• Overcomplicating with recursion