Sodoku classical backtracking

Sodoku classical backtracking

backtracking the same as 8 queens and prime number circle

//pass
#include
#include
using namespace std;

#define N 9
 int grid[N][N] = {{3, 0, 6, 5, 0, 8, 4, 0, 0},
                      {5, 2, 0, 0, 0, 0, 0, 0, 0},
                      {0, 8, 7, 0, 0, 0, 0, 3, 1},
                      {0, 0, 3, 0, 1, 0, 0, 8, 0},
                      {9, 0, 0, 8, 6, 3, 0, 0, 5},
                      {0, 5, 0, 0, 9, 0, 6, 0, 0},
                      {1, 3, 0, 0, 0, 0, 2, 5, 0},
                      {0, 0, 0, 0, 0, 0, 0, 7, 4},
                      {0, 0, 5, 2, 0, 6, 3, 0, 0}};

/* Returns whether any assigned entry n the specified row matches 
   the given number. */
bool UsedInRow(int grid[N][N], int row, int num)
{
    for (int col = 0; col < N; col++)
    if (grid[row][col] == num)
        return true;
    return false;
}

/* Returns whether any assigned entry in the specified column matches 
   the given number. */
bool UsedInCol(int grid[N][N], int col, int num)
{
    for (int row = 0; row < N; row++)
        if (grid[row][col] == num)
            return true;
    return false;
}

/* Returns whether any assigned entry within the specified 3x3 box matches 
   the given number. */
bool UsedInBox(int grid[N][N], int boxStartRow, int boxStartCol, int num)
{
    for (int row = 0; row < 3; row++)
        for (int col = 0; col < 3; col++)
            if (grid[row+boxStartRow][col+boxStartCol] == num)
                return true;
    return false;
}

/* Returns whether it will be legal to assign num to the given row,col location. 
 */
bool isSafe(int row, int col, int num)
{
    return !UsedInRow(grid, row, num) && !UsedInCol(grid, col, num) &&
       !UsedInBox(grid, row - row % 3 , col - col % 3, num);
}


bool SodokuSolver(int seq){
	//int seq=row*9+col;
	int row=seq/9;
	int col=seq%9;
	while(grid[row][col]!=0&&row<=8&&col<=8){
		//move to next position
		seq++;
		row=seq/9;
		col=seq%9; 
	}
	//if row=9,col=0,it means we have finish its
	if(seq==81) return true;//Indicate that we have finish all the 81 blocks 
	else{
		//grid[row][col]==0,So we should try every number from 1-9 and check
		for(int num=1;num<10;num++){
			if(isSafe(row,col,num)){//if it is safe and not only it is safe it will finish the whole bolck. if it can not fisnish the whole block ,it must roll back
				//move to next position
				grid[row][col]=num;
				if(SodokuSolver(seq+1))	return true;
				row=seq/9;
				col=seq%9; 
				grid[row][col]=0;
			}
		}
		return false;
	}
}

void printGrid(int grid[N][N])
{
    for (int row = 0; row < N; row++)
    {
        for (int col = 0; col < N; col++)
            cout<