C++ :

#include<bits/stdc++.h>
using namespace std;
int a[10][10],r[10][10],c[10][10],g[10][10];
char s[10][10];
void prin()
{
	for (int i=1;i<=9;i++){
		for (int j=1;j<=9;j++) cout<<a[i][j];
		cout <<endl;
	}
	  
}
void dfs(int x,int y)
{
	//if (x<2) cout << endl << x <<" "<<y;
	if (x > 9){
		prin();return;
	}
	if (a[x][y]){
		if (y == 9)  dfs(x+1,1);
		else dfs(x,y+1);
		
	}
	else{
		int k = 3 * ((x - 1) / 3) + (y - 1) / 3 + 1;
		for (int i=1;i<=9;i++)
		   if (!r[x][i] && !c[y][i] && !g[k][i]){
		   	   a[x][y] = i;
		   	   r[x][i] = 1;
		   	   c[y][i] = 1;
		   	   g[k][i] = 1;
		   	   if (y == 9)  dfs(x+1,1);
		   	   else  dfs(x,y+1);
		   	   	a[x][y] = 0;
		   	    r[x][i] = 0;
		   	    c[y][i] = 0;
		   	    g[k][i] = 0;
		   }
	}
}
int main()
{
    for (int i=1;i<=9;i++){
    	cin >> s[i];
    	for (int j=1;j<=9;j++){
    		if (s[i][j-1] != '?'){
    			int x = s[i][j-1]-'0';
    			a[i][j]= x;
    			r[i][x] = 1;
    			c[j][x] = 1;
    			int k = 3 * ((i - 1) / 3) + (j - 1) / 3 + 1;
    			g[k][x] = 1;
			} 
		}
	}
	//for (int i=1;i<=9;i++) 
	   //for (int j=1;j<=9;j++)  if (g[i][j]) cout << i << j <<endl;
    dfs(1,1); 	    
    return 0;
}