Question:
Write an algorithm such that if an element in an MxN matrix is 0, its entire row and column is set to 0.
Solution:

#include <iostream>
#include <string.h>

using namespace std;


void transform(int **data, int M,int N){
 int *prev = new int[N];
 for(int i=0;i<N;++i)
  prev[i]=1;
 for(int i=0;i<M;++i){
  bool setrow = false;
  for(int j=0;j<N;++j){

   bool setcol=false;
   if( prev[j] == 1 && data[i][j] == 0  ){
    prev[j] = 0;
    setrow = true;
    setcol = true;

   } else if (prev[j]==0 && data[i][j]  ){
    data[i][j] = 0;
   }

   if (setcol){
    for(int k=i;k>=0;--k){
     data[k][j]=0;
    }
   }
  }
  if (setrow){
   for(int k=0;k<N;++k){
    data[i][k] = 0;
   }
  }
 }
 delete []prev;
}

void print(int **data, int M, int N){
 for(int i=0;i<M;++i){
  for(int j=0;j<N;++j){
   cout<<data[i][j]<<" ";
  }
  cout<<endl;
 }
}

int main() {
 int **data;
 data = new int* [4];
 for(int i=0;i<4;++i){
  data[i] = new int[5];
 }
 for(int i=0;i<4;++i)
  for(int j=0;j<5;++j)
   data[i][j]=1;

 data[0][3] = 0;
 data[1][2] = 0;
 data[2][3] = 0;

 print(data,4,5);
 transform(data,4,5);
 cout<<"------------------"<<endl;
 print(data,4,5);
        //release memory
       for(int i=0;i<5;++i){
           delete[] data[i];
       }
       delete[] data;
 return 0;
}

Coding Question: rotate a NxN matrix by 90 degrees in-place

Question:
Given an image represented by an NxN matrix, where each pixel in the image is 4 bytes, write a method to rotate the image by 90 degrees. Can you do this in place?

Solution:

#include <iostream>
using namespace std;

void rotate90(int **array, int N){
    for(int i=0;i<N/2;++i){
        for(int j=i;j<N-1-i;++j){
	    int t1=array[j][N-1-i];
	    array[j][N-1-i] = array[i][j];

            int t2=array[N-1-i][N-1-j];
            array[N-1-i][N-1-j] = t1;

            t1 = array[N-1-j][i];
            array[N-1-j][i] = t2;

            array[i][j] = t1;
       }
    }
}

int main() {
    int **matrix;
    matrix = new int*[5];
    for(int i=0;i<5;++i)
        matrix[i] = new int[5];

    int count=0;
    for(int i=0;i<5;++i)
        for(int j=0;j<5;++j){
        matrix[i][j] = count++;
		}

    for(int i=0;i<5;++i){
       for(int j=0;j<5;++j){
           cout<<matrix[i][j]<<" ";
       }
       cout<<endl;
    }
    cout<<"----------------"<<endl;
    rotate90(matrix,5);
    for(int i=0;i<5;++i){
        for(int j=0;j<5;++j){
            cout<<matrix[i][j]<<" ";
        }
        cout<<endl;
    }
    //release memory
    for(int i=0;i<5;++i){
       delete[] matrix[i];
    }
    delete[] matrix;
    cout << "" << endl; // prints 
    return 0;
}