Sudoku backtracking problem

general
,
1

I’m only getting the first subgrid solved in the output, can anyone point out what’s wrong here?

#include <bits/stdc++.h>
#define vi vector<int>
#define dvi vector<vector<int>>
#define b begin
#define e end
#define ff first
#define ss second
#define viit vector<int>::iterator

using namespace std;


void peek (dvi vec) {
	for(auto i:vec) {
		for(auto j:i) cout << j;
		cout << endl;
	}
}

vi options (dvi grid, int i, int j, int n) {
  vi o_vec;
  if(grid[i][j]) return o_vec;
  for(int m=1;m<=9;m++) o_vec.push_back(m);
  for(int x=0;x<n;x++) {
  	viit it = find(o_vec.b(),o_vec.e(),grid[x][j]);
  	if(it!=o_vec.e()) o_vec.erase(it);
  }
  for(int y=0;y<n;y++) {
    viit it = find(o_vec.b(),o_vec.e(),grid[i][y]);
  	if(it!=o_vec.e()) o_vec.erase(it);                
  }
  int d=3;
  int sub = n/d, si = (i/sub)*sub, sj = (j/sub)*sub;
  for(int x=si;x<si+sub;x++) {
  	for(int y=sj;y<sj+sub;y++) {
  	  viit it = find(o_vec.b(),o_vec.e(),grid[x][y]);
  		if(it!=o_vec.e()) o_vec.erase(it);
  	}
  }
  return o_vec;
}

bool sudoku (dvi& grid, int j, int n) {
	if(j==n) return true;
	else {
		for(int i=0;i<n;i++) {
			vi opt = options(grid,i,j,n);
			if(opt.size()) {
				for(int k=0;k<opt.size();k++) {
					grid[i][j] = opt[k];
					if(sudoku(grid,j+1,n)) return true;
				}
				grid[i][j] = 0;
			}
		}
	}
	return false;
}

void sudoku_util(dvi& grid) {
	int n = grid.size();
	sudoku(grid,0,n);
}

int main () {
	dvi grid = {{3, 0, 6, 5, 0, 8, 4, 0, 0},  
              {5, 2, 0, 0, 0, 0, 0, 0, 0},  
              {0, 8, 7, 0, 0, 0, 0, 3, 1},  
              {0, 0, 3, 0, 1, 0, 0, 8, 0},  
              {9, 0, 0, 8, 6, 3, 0, 0, 5},  
              {0, 5, 0, 0, 9, 0, 6, 0, 0},  
              {1, 3, 0, 0, 0, 0, 2, 5, 0},  
              {0, 0, 0, 0, 0, 0, 0, 7, 4},  
              {0, 0, 5, 2, 0, 6, 3, 0, 0}};
  sudoku_util(grid);
  peek(grid);
	return 0;
}

Output:

316528490
529104706
487000031
003010080
900863005
050090600
130000250
000000074
005206300
2

can you please share the problem url so that I can understand the problem it looks cryptic

3

the unsolved sudoku is given in the main method, and the aim is to solve the sudoku by replacing all 0s by numbers from 1-9

4