TheAlgorithms-C-Plus-Plus/backtracking/n_queens_all_solution_optimised.cpp

#include <iostream>
#define n 4
#define inc_loop(var, start, stop, step) for (int var=start; var <= stop; var+=step)
#define dec_loop(var, start, stop, step) for (int var=start; var >= stop; var-=step)
void PrintSol(int Board[n][n]) {
    inc_loop(i,0,n-1,1) {
        inc_loop(j,0,n-1,1)
            std::cout << Board[i][j] << " ";
        std::cout << std::endl;
    }
    std::cout << std::endl;
    if (n%2==0 || (n%2==1 && Board[n/2+1][0]!=1)){
        inc_loop(i,0,n-1,1){
            dec_loop(j,n-1,0,1)
                std::cout<<Board[i][j]<<" ";
            std::cout<<std::endl;
        }
        std::cout<<std::endl;
    }
}

bool CanIMove(int Board[n][n], int row, int col) {
    /// check in the row
    for (int i = 0; i < col; i++) {
        if (Board[row][i] == 1)
            return false;
    }
    /// check the first diagonal
    for (int i = row, j = col; i >= 0 && j >= 0; i--, j--) {
        if (Board[i][j] == 1)
            return false;
    }
    /// check the second diagonal
    for (int i = row, j = col; i <= n - 1 && j >= 0; i++, j--) {
        if (Board[i][j] == 1)
            return false;
    }
    return true;
}

void NQueenSol(int Board[n][n], int col) {
    if (col >= n) {
        PrintSol(Board);
        return;
    }
    inc_loop(i,0,n-1,1) {
        if (CanIMove(Board, i, col)) {
            Board[i][col] = 1;
            NQueenSol(Board, col + 1);
            Board[i][col] = 0;
        }
    }
}

int main() {
    int Board[n][n] = {0};
    if (n%2==0) {
        inc_loop(i,0,n/2-1,1) {
            if (CanIMove(Board, i, 0)) {
                Board[i][0] = 1;
                NQueenSol(Board,1);
                Board[i][0] = 0;
            }
        }
    }
    else {
        inc_loop(i,0,n/2,1) {
            if (CanIMove(Board, i,0)) {
                Board[i][0] = 1;
                NQueenSol(Board,1);
                Board[i][0] = 0;
            }
        }
    }
    return 0;
}