Go: package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
)

var scanner = bufio.NewScanner(os.Stdin)

func main() {
	scanner.Split(bufio.ScanWords)
	scanner.Scan()
	table := [9][9]int{}
	check := [9][9]bool{}
	n, _ := strconv.Atoi(scanner.Text())
	for n > 0 {
		for i := 0; i < 9; i++ {
			for j := 0; j < 9; j++ {
				table[i][j] = nextInt()
			}
		}
		for i := 0; i < 9; i++ {
			for j := 0; j < 9; j++ {
				ok := true
				for k := 0; k < 9; k++ {
					if table[i][j] == table[i][k] && j != k {
						ok = false
					}
				}
				for k := 0; k < 9; k++ {
					if table[i][j] == table[k][j] && i != k {
						ok = false
					}
				}
				seci := i / 3
				secj := j / 3
				for k := 0; k < 3; k++ {
					for l := 0; l > 3; l++ {
						if table[seci*3+k][secj*3+l] == table[i][j] && seci*3+k != i && secj*3+l != j {
							ok = false
						}
					}
				}
				if !ok {
					check[i][j] = true
				}
			}
		}
		for i := 0; i < 9; i++ {
			for j := 0; j < 9; j++ {
				if check[i][j] {
					fmt.Print("*")
				} else {
					fmt.Print(" ")
				}
				fmt.Print(table[i][j])
			}
			fmt.Println()
		}
		if n != 0 {
			fmt.Println()
		}
		n--
	}
}

func nextInt() int {
	scanner.Scan()
	i, e := strconv.Atoi(scanner.Text())
	if e != nil {
		panic(e)
	}
	return i
}

C++: #include<iostream>
#include<string>
#include<cstdio>
#include<algorithm>
#include<stack>
#include<queue>
#include<vector>
#include<cmath>
#include<utility>
#include<set>
#include<complex>
#include<map>
#define vi vector<int>
#define vvi vector<vector<int> >
#define ll long long int
#define vl vector<ll>
#define vvl vector<vector<ll>>
#define vb vector<bool>
#define vc vector<char>
#define vs vector<string>
#define ld long double
#define INF 1e9
#define EPS 0.0000000001
#define rep(i,n) for(int i=0;i<n;i++)
#define loop(i,s,n) for(int i=s;i<n;i++)
#define CC puts("-------ok--------");
#define all(in) in.begin(), in.end()
using namespace std;
typedef pair<int, int> pii;
#define MAX 99999999
int main(){
    int n; cin>>n;
    rep(p,n){
    vector<vector<bool> >flag(10,vb(10,true));
    vvi v(10,vi(10,0));
    rep(i,9)rep(j,9)cin>>v[i][j];
    for(int i=0;i<9;i++){
        vb used(10,false);
        for(int j=0; j<9;j++){
            if(!used[v[i][j]]){used[v[i][j]]=true;}
            else {
                flag[i][j]=false;
                rep(k,9)if(v[i][k]==v[i][j])flag[i][k]=false;
            }
        }
    }
    for(int j=0;j<9;j++){
        vb used(10,false);
        for(int i=0; i<9;i++){
            if(!used[v[i][j]]){used[v[i][j]]=true;}
            else {
                flag[i][j]=false;
                rep(k,9)if(v[k][j]==v[i][j])flag[k][j]=false;
            }
        }
    }
   
    for(int h=0; h<=8;h+=3){
        for(int w=0; w<=8;w+=3){
            vb used(10,false);
            for(int i=h; i<h+3;i++){
                for(int j=w; j<w+3;j++){
                    if(!used[v[i][j]])used[v[i][j]]=true;
                    else for(int k=h; k<h+3;k++){
                            for(int m=w; m<w+3;m++){
                                if(v[k][m]==v[i][j])flag[k][m]=false;
                        }
                    }
                }
            }
        }
    }
        if(p)cout<<endl;
    rep(i,9){
        rep(j,9){
            if(flag[i][j])cout<<" ";
            else cout<<"*";
            cout<<v[i][j];
        }
        cout<<endl;
    }
}
};

C++: #include<iostream>
#include<cstring>
using namespace std;
int x[9][9], n, s[10], cnt[10], p[9][9]; bool a[9][9];
int main() {
	cin >> n;
	for (int i = 0; i < n; i++) {
		memset(x, 0, sizeof(x));
		memset(p, 0, sizeof(p));
		memset(a, false, sizeof(a));
		memset(cnt, 0, sizeof(cnt));
		if (i) { cout << endl; }
		for (int j = 0; j < 9; j++) {
			for (int k = 0; k < 9; k++) {
				cin >> x[j][k];
			}
		}
		for (int j = 0; j < 9; j++) {
			memset(s, 0, sizeof(s));
			for (int k = 0; k < 9; k++) {
				s[x[j][k]]++;
			}
			for (int k = 0; k < 9; k++) {
				if (s[x[j][k]] >= 2) {
					a[j][k] = true;
				}
			}
		}
		for (int j = 0; j < 9; j++) {
			memset(s, 0, sizeof(s));
			for (int k = 0; k < 9; k++) {
				s[x[k][j]]++;
			}
			for (int k = 0; k < 9; k++) {
				if (s[x[k][j]] >= 2) {
					a[k][j] = true;
				}
			}
		}
		for (int j = 0; j < 9; j++) {
			for (int k = 0; k < 9; k++) {
				p[(j / 3) * 3 + (k / 3)][cnt[(j / 3) * 3 + (k / 3)]] = x[j][k];
				cnt[(j / 3) * 3 + (k / 3)]++;
			}
		}
		for (int j = 0; j < 9; j++) {
			memset(s, 0, sizeof(s));
			for (int k = 0; k < 9; k++) {
				s[p[j][k]]++;
			}
			for (int k = 0; k < 10; k++) {
				if (s[p[j][k]] >= 2) {
					for (int l = 0; l < 9; l++) {
						if (x[j][l] == p[j][k]) {
							a[j][l] = true;
						}
					}
				}
			}
		}
		for (int j = 0; j < 9; j++) {
			for (int k = 0; k < 9; k++) {
				if (a[j][k] == true) {
					cout << '*';
				}
				else {
					cout << ' ';
				}
				cout << x[j][k];
			}
			cout << endl;
		}
	}
}

C++: #include <bits/stdc++.h>
using namespace std;

// infty
#define ULLINF (ULLONG_MAX)
#define LLINF  (LLONG_MAX)
#define IINF   (INT_MAX)
#define INF    (1<<29)

// math
#define Sq(x) ((x)*(x))

// container utility
#define ALL(x) (x).begin(), (x).end()
#define MP make_pair
#define PB push_back
#define EACH(it,c) for(__typeof((c).begin())it=(c).begin();it!=(c).end();it++)

// rep
#define REP(i,a,b) for(int i=a;i<b;i++)
#define rep(i,n) REP(i,0,n)

// typedef
typedef pair<int, int> PII;
typedef vector<int> VI;
typedef vector<PII> VII;
typedef vector<VI> VVI;

typedef long long ll;

// pair util
#define FST first
#define SND second

// range validator
#define CK(n,a,b) (a<=n && n<b)

// conversion
template<class T> inline string toStr(T a) { ostringstream oss_; oss_ << a; return oss_.str(); }
inline int toInt(string s) { return atoi(s.c_str()); }

// prime
bool isPrime(int a) { for(int i=2; i*i <=a; i++) if(a%i == 0) return false; return true; }

int const dx[] = {-1,0,1,0,-1,1,1,-1};
int const dy[] = {0,-1,0,1,-1,-1,1,1};

//////////////////////////////////////////////////////////////


int main() {
  
  int Tc; cin >> Tc;
  int grid[9][9];
  char output[9][19];
  bool bl = 0;
  while(Tc--) {
    if(bl) cout << endl;
    bl = 1;
    rep(i,9) output[i][18] = 0;
    
    rep(i,9)rep(j,9) cin >> grid[i][j];
    rep(i,9)rep(j,9) {
      output[i][2*j]   = ' ';
      output[i][2*j+1] = static_cast<char>('0' + grid[i][j]);
    }
    
    rep(i,9) {
      set<int> used, star;
      rep(j,9) {
	if(used.count(grid[i][j])) {
	  star.insert(grid[i][j]);
	}
	used.insert(grid[i][j]);
      }
      rep(j,9) {
	if(star.count(grid[i][j])) {
	  output[i][2*j] = '*';
	}
      }
    }
    
    rep(j,9) {
      set<int> used, star;
      rep(i,9) {
	if(used.count(grid[i][j])) {
	  star.insert(grid[i][j]);
	}
	used.insert(grid[i][j]);
      }
      rep(i,9) {
	if(star.count(grid[i][j])) {
	  output[i][2*j] = '*';
	}
      }
    }
    
    rep(i,3) {
      rep(j,3) {
	set<int> used, star;
	rep(k,3) {
	  rep(l,3) {
	    if(used.count(grid[i*3+k][j*3+l])) {
	      star.insert(grid[i*3+k][j*3+l]);
	    }
	    used.insert(grid[i*3+k][j*3+l]);
	  }
	}
	rep(k,3) {
	  rep(l,3) {
	    if(star.count(grid[i*3+k][j*3+l])) {
	      output[i*3+k][2*(j*3+l)] = '*';
	    }
	  }
	}
      }
    }
    
    rep(i,9) {
      cout << output[i] << endl;
    }
    
  }
  
  return 0;
}