Sudoku Solver

sudoku.cpp

#include<iostream>
using namespace std;
int sudoku[9][9],ptr[162],xstart[9]={0,3,6,0,3,6,0,3,6}, ystart[9]={0,0,0,3,3,3,6,6,6};
int valid(){
    int valid=1;
    int hashtable[10];
    for(int i=0;i<9;i++){
        for(int j=0;j<9;j++){
            for(int k=j+1;k<9;k++){
	        if(sudoku[i][j]==0) continue;
	        if(sudoku[i][j]==sudoku[i][k]){
                    return 0;
                }
            }
        }
    }
    
    for(int i=0;i<9;i++){
        for(int j=0;j<9;j++){
            for(int k=j+1;k<9;k++){	
                if(sudoku[j][i]==0) continue;
                if(sudoku[j][i]==sudoku[k][i]) {
		    return 0;
	            }
            }
        }
    }
    for(int i=0;i<9;i++){	
        for(int x=0;x<=9;x++) 
	        hashtable[x]=0;
        for(int j=xstart[i];j<xstart[i]+3;j++)
	        for(int k=ystart[i];k<ystart[i]+3;k++)
		        hashtable[sudoku[j][k]]++;	
        for(int x=1;x<=9;x++)
	        if(hashtable[x]>1) {return 0;}
    }
    return 1;
}


int main(){	
	int k,val;
	cout<<"Enter the sudoku problem, use 0 for blank:\n"<<endl;
	for(int i=0;i<9;i++)
		for(int j=0;j<9;j++)
			cin>>sudoku[i][j];
	while(1){
        k=0;
        for(int i=0;i<9;i++)
            for(int j=0;j<9;j++)
                if(sudoku[i][j]==0){
                    ptr[k++]=i;
                    ptr[k++]=j;
                }
        if(!valid()) {cout<<"\nIncorrect puzzle\n\n";return 0;}

        if(k==0) break;

        int i=0;

        while(i<(k/2)){	
            while(sudoku[ptr[2*i]][ptr[2*i+1]]<10){
                sudoku[ptr[2*i]][ptr[2*i+1]]++;
                if(valid())
                    break;
            }
            if(sudoku[ptr[2*i]][ptr[2*i+1]]>9){
                sudoku[ptr[2*i]][ptr[2*i+1]]=0;
                if(i==0) {
                    i++;
                    continue;
                }
                else {
                    i--;
                    continue;
                }
            }
            else i++;
        }
    }
    cout<<endl<<"The solution for the given problem is:\n"<<endl;
    for(int i=0;i<9;i++){
        for(int j=0;j<9; j++)
	        cout<<sudoku[i][j]<<" ";
        cout<<endl;
    }
    cout<<endl;
    return 0;	
}