Solution to HackerRank Olympics sudoku puzzle in C++

sudoku.cpp

#include<iostream>
#include<vector>
#include<set>
#include<math.h>

using namespace std;

int getSector(int row, int col) {
    return (row/3)*3+(col/3);
}

bool valid(int grid[9][9], int row, int col) {
    for (int i = 0; i < 9; i++) {
        if (grid[row][i] == grid[row][col] && i != col) return false;
        if (grid[i][col] == grid[row][col] && i != row) return false;
    }
    for (int i = 0; i < 9; i++) {
        for (int j = 0; j < 9; j++) {
            if (getSector(row, col) == getSector(i, j) && row != i && col != j && grid[i][j] == grid[row][col]) return false;
        }
    }

    return true;
}

/* Head ends here */
void sudoku_solve(int grid[9][9],set<int> set) {
    //your logic here
    int forward = 1;
    for (int idx = 0; idx < 81;) {
        int row = floor(idx/9);
        int col = fmod(idx,9);
        if (set.count(idx)>0) {
            idx += 1*forward;
        } else {
            grid[row][col]++;
            if (grid[row][col] == 10) {
                grid[row][col] = 0;
                forward = -1;
                idx--;
            }
            if (valid(grid, row, col)) {
                forward = 1;
                idx++;
            }
        }
    }
    for (int i = 0; i < 9; i++) {
        for (int j = 0; j < 9; j++) {
            cout << grid[i][j] << " ";
        }
        cout << endl;
    }
}

/* Tail starts here */
int main() {
    int n, board[9][9];
    set<int> set;
    cin >> n;
    for(int i=0;i<n;i++) {
        for(int j=0;j<9;j++) {
            for(int k=0;k<9;k++) {
                board[j][k] = 0;
                cin >> board[j][k];
                if ( board[j][k] != 0 ) set.insert(j*9+k);
            }
        }
        sudoku_solve(board,set);
    }
    return 0;
}