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#include <iostream>
#include <algorithm>
#include <ctime>
const unsigned SIZE=9;
typedef unsigned char sudoku[SIZE][SIZE];
bool check(sudoku matrix,unsigned x,unsigned y){
unsigned char val=matrix[x][y];
for (unsigned a=0;a<x;a++)
if (matrix[a][y]==val)
return 0;
for (unsigned a=x+1;a<SIZE;a++)
if (matrix[a][y]==val)
return 0;
for (unsigned a=0;a<y;a++)
if (matrix[x][a]==val)
return 0;
for (unsigned a=y+1;a<SIZE;a++)
if (matrix[x][a]==val)
return 0;
unsigned startx=x/(SIZE/3)*3,
starty=y/(SIZE/3)*3,
endx=startx+SIZE/3,
endy=starty+SIZE/3;
for (unsigned a=startx;a<endx;a++){
for (unsigned b=starty;b<endy;b++){
if (a!=x && b!=y && matrix[a][b]==val)
return 0;
}
}
return 1;
}
void printMatrix(sudoku matrix){
for (unsigned b=0;b<SIZE;b++){
for (unsigned a=0;a<SIZE;a++){
if (matrix[a][b])
std::cout <<(int)matrix[a][b];
else
std::cout <<'_';
if (a && a%(SIZE/3)==SIZE/31)
std::cout <<' ';
}
std::cout <<std::endl;
if (b && b%(SIZE/3)==SIZE/31)
std::cout <<std::endl;
}
}
void transpose(sudoku matrix){
for (unsigned y=0;y<SIZE1;y++){
for (unsigned x=y+1;x<SIZE;x++){
std::swap(matrix[x][y],matrix[y][x]);
}
}
}
unsigned solution_time=0;
bool solve(sudoku matrix,unsigned pos=0){
unsigned x=pos%SIZE,
y=pos/SIZE;
if (y>=SIZE)
return 1;
if (matrix[x][y])
return solve(matrix,pos+1);
for (unsigned a=1;a<=SIZE;a++){
solution_time++;
matrix[x][y]=a;
if (check(matrix,x,y) && solve(matrix,pos+1))
return 1;
}
matrix[x][y]=0;
return 0;
}
int main(){
sudoku matrix=
{
1,0,0, 0,0,7, 0,9,0,
0,3,0, 0,2,0, 0,0,8,
0,0,9, 6,0,0, 5,0,0,
0,0,5, 3,0,0, 9,0,0,
0,1,0, 0,8,0, 0,0,2,
6,0,0, 0,0,4, 0,0,0,
3,0,0, 0,0,0, 0,1,0,
0,4,0, 0,0,0, 0,0,7,
0,0,7, 0,0,0, 3,0,0,
};
clock_t t0,t1;
t0=clock();
transpose(matrix);
if (!solve(matrix))
std::cout <<"Unsolvable!"<<std::endl;
else
printMatrix(matrix);
t1=clock();
std::cout <<"Solved in "<<solution_time<<" iterations."<<std::endl;
std::cout <<double(t1t0)/(double(CLOCKS_PER_SEC)/1000.0)<<" ms"<<std::endl;
return 0;
}
 