UVa 989 - Sudoku - Lento

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <vector>
#include <map>
#include <set>
#include <cmath>
#include <bitset>

using namespace std;

#define forn(i,n) for(int i=0;i<(int)(n);i++)
#define forsn(i,s,n) for(int i=(int)(s);i<(int)(n);i++)
#define forall(i,c) for(typeof((c).begin()) i=(c).begin();i!=(c).end();i++)
#define dforn(i,n) for(int i=((int)(n)-1);i>=0;i--)
#define dforsn(i,s,n) for(int i=((int)(n)-1);i>=(int)(n);i--)
#define esta(i,c) ((c).find(i) != (c).end())
#define dbg(x) cerr << #x << " = " << x << endl;
#define raya cerr << string(80,'=') << endl;

typedef long long tint;
typedef pair<int,int> pii;
typedef vector<int> vi;
typedef vector< pair<int,int> > vii;

int n, nrows, ncols, m[9][9];
int zr[81],zc[81],z;
int inRow[9][10],inBlock[9][10],inCol[9][10];

bool solFound = false;

bool checkSudoku(){
    forn(i,nrows) forsn(j,1,nrows+1)
        if(inRow[i][j] != 1 || inCol[i][j] != 1 || inBlock[i][j] != 1) return false;
    return true;
}

void backtrack(int cz){
    if(checkSudoku()){
        solFound = true;
    }else{
        if(cz == z) return;
        int nr = zr[cz], nc = zc[cz];

        forsn(i,1,n*n+1){
            if(!inRow[nr][i] && !inCol[nc][i] && !inBlock[n*(nr/n)+nc/n][i]){
                m[nr][nc] = i;
                inRow[nr][i] = inCol[nc][i] = inBlock[n*(nr/n)+nc/n][i] = 1;
                backtrack(cz+1);

                if(solFound) return;
                inRow[nr][i] = inCol[nc][i] = inBlock[n*(nr/n)+nc/n][i] = 0;
            }
        }

        m[nr][nc] = 0;
    }
}

int main(){
    #ifdef JUAMPI
        freopen("989.in","r",stdin);
    #endif

    bool flag = true;
    while(scanf("%d",&n) == 1){
        if(flag) flag = false; else putchar('\n');
        nrows = ncols = n*n;

        z = 0;

        memset(inRow,0,sizeof(inRow));
        memset(inCol,0,sizeof(inCol));
        memset(inBlock,0,sizeof(inBlock));

        forn(i,nrows)
        forn(j,ncols){
            scanf("%d",&m[i][j]);
            int v = m[i][j];
            if(v==0){
                zr[z] = i; zc[z] = j; z++;
            }else{
                inRow[i][v]++; inCol[j][v]++; inBlock[n*(i/n)+j/n][v]++;
            }
        }

        solFound = false;
        backtrack(0);

        if(solFound){
            forn(i,nrows){
                forn(j,ncols){
                    putchar(m[i][j]+'0');
                    if(j < n*n-1) putchar(' ');
                }
                putchar('\n');
            }
        }else{
            printf("NO SOLUTION\n");
        }
    }

    return 0;
}