Set matrix zeros - c++11

Question

" I am trying to write algorithm which sets ith row jth coumn to zeros
in case of A[i][j]=0."
" I tried by printing the elements of matrix A While the third for loop
is assigning zeros to the jth column of matrix as well as after the
completion of whole function. Surprisingly in the first case allthe
elements of first column are
zero but in the second case last element of column is 1.""
#include <iostream>
#include<string>
#include<vector>
using namespace std;
/*FUNCTION TO FIND ZEROS AND ASSIGN ith AND jth row AND columns zero
*/
void setZeroes(vector<vector<int> > &A) {
string a,b;/* string a is created to store indexes of rows whose
elemnts are to be converted to zero if atleast one element in the
row is occupied by zero and similarly b is for columns*/
/*for loop to find the indexes of zero elements*/
for(int i=0;i<A.size();i++){
for(int j=0;j<A[0].size();j++){
if(A[i][j]==0){
/*append function stores the indexes in strings*/
a.append(to_string(i));b.append(to_string(j));}
}
}
/*for loop to assign zeros to the elements of ith row*/
for(int i=0;i<a.length();i++){
int j=atoi(&a[i]),k=0;
while(k<A[j].size()){
A[j][k]=0;
k++;}
}
/*for loop to assign zeros to the elements of jth column*/
for(int i=0;i<b.length();i++){
int j=atoi(&b[i]),k=0;
while(k<A.size()){
A[k][j]=0; //every element in A is assigned zero at this point
k++;
}
}
}
//driver function
int main()
{
vector<vector<int>>A={{0,0},{1,1}};
//invoking the setZeroes function
setZeroes(A); for(int i=0;i<A.size();i++){
for(int j=0;j<A[0].size();j++){
cout<<A[i][j]<<" ";// (error)Here A[1][0] is printed as 1
}
cout<<endl;
}
return 0;
}
Input:[
[0, 0]
[1, 1]
]
Expected:[
[0, 0]
[0, 0]
]
Actual:
[
[0, 0]
[1, 0]
]

Answer 1

This atoi(&a[i]) and that atoi(&b[i]) are wrong.
You suppose that a and b keep indices in range <0,9>. So to access them you can substract 48 (ascii code of 0 char):
int j = a[i] - 48; // the same with b[i]
or you can create one-character string, then use atoi to convert it into integer:
int j = atoi( string(1,a[i]).c_str() ); // this ctor takes one char and creates string
By doing atoi(&a[i]) you are creating integer value starting at i-item to the end of string - it is not what you want.
If index can have two or more digits, you need to use some different container to store them, for example vector of string.

Answer 2

**javascript**
let setZero = function(matrix) {
let m = matrix.length;
let n = (matrix[0] || []).length;
for (let i = 0; i < m; i++) {
for (let j = 0; j < n; j++) {
if (matrix[i][j] === 0) {
left(i, j, m, n, matrix);
right(i, j, m, n, matrix);
up(i, j, m, n, matrix);
down(i, j, m, n, matrix);
} else if (matrix[i][j] === '#') {
matrix[i][j] = 0;
}
}
}
};
let left = function (i, j, m, n, matrix) {
for (var k = j - 1; k >= 0; k--) {
matrix[i][k] = 0;
}
};
let right = function (i, j, m, n, matrix) {
for (var k = j + 1; k < n; k++) {
matrix[i][k] = matrix[i][k] === 0 ? 0 : '#';
}
};
let up = function (i, j, m, n, matrix) {
for (var k = i - 1; k >= 0; k--) {
matrix[k][j] = 0;
}
};
let down = function (i, j, m, n, matrix) {
for (var k = i + 1; k < m; k++) {
matrix[k][j] = matrix[k][j] === 0 ? 0 : '#';
}
};