Eight queens problem checking

t13e13.queens.cpp

// t13e13.queens.cpp
// juanfc 2023-11-23
// https://gist.github.com/9c722f7ca79a44e778a74a63395ef04e

#include <iostream>
#include <array>
using namespace std;

const int N = 8;
const char X = '#';
const int NQUEENS = N;
typedef array<array<char,N>,N> TChessboard;

int main()
{
    void test(string);

    test(
        "#       " // 0
        "      # " // 1
        "    #   " // 2
        "       #" // 3
        " #      " // 4
        "   #    " // 5
        "     #  " // 6
        "  #     " // 7
      // 01234567
    );

    test(
        "  #     " // 0
        "     #  " // 1
        "       #" // 2
        "#       " // 3
        "   #    " // 4
        "      # " // 5
        "    #   " // 6
        " #      " // 7
      // 01234567
    );

    test(
        "  #     " // 0
        "  #     " // 1
        "       #" // 2
        "#       " // 3
        "   #    " // 4
        "      # " // 5
        "    #   " // 6
        " #      " // 7
      // 01234567
    );

    return 0;
}

bool noThreat(TChessboard m)
{

    bool checkCell(TChessboard m, int row, int col);

    int cnt = 0;
    bool ok = true;
    int i = 0;
    while (i < N and cnt <= NQUEENS and ok) {
        int j = 0;
        while (j < N and cnt <= NQUEENS and ok) {
            if (m[i][j] == X) {
                ok = checkCell(m, i, j);
            }
            ++j;
        }
        ++i;
    }
    return ok;

}

bool checkCell(TChessboard m, int row, int col)
{
    bool ok = true;
    // check column
    int x = 0;
    while (x < N and (x == row or m[x][col] != X))
        ++x;
    ok = x == N;

    // check row
    x = 0;
    while (ok and x < N and (x == col or m[row][x] != X))
        ++x;
    ok = x == N;


    // cout << row << ", " << col << endl;

    if (ok) {
        // \ diag zone right
        if (row<=col) {
            x = 0;
            while (col-row+x < N and (x == row or m[x][col-row+x] != X)) {
                // cout << x << ", " << col-row+x << endl;
                ++x;
            }
            ok = col-row+x == N;
        } else{
        // \ diag zone left
            x = 0;
            while (row-col+x < N and (x == col or m[row-col+x][x] != X)) {
                // cout << row-col+x << ", " << x << endl;
                ++x;
            }
            ok = row-col+x == N;
        }
    }

    if (ok) {
        // / upper
        if (row+col<N) {
            x = 0;
            while (col+row-x >= 0 and (x == col or m[col+row-x][x] != X)) {
                // cout << col+row-x << ", " << x << endl;
                ++x;
            }
            ok = col+row-x < 0;
        } else{
        // / lower
            x = 0;
            while (col-(N-1-row)+x < N and (N-1-x == row or m[N-1-x][col-(N-1-row)+x] != X)) {
                // cout << N-1-x << ", " << col-(N-1-row)+x << endl;
                ++x;
            }
            ok = col-(N-1-row)+x == N;
        }
    }

    return ok;
}

namespace std {
  template <typename _CharT, typename _Traits>
  inline basic_ostream<_CharT, _Traits> &
  tab(basic_ostream<_CharT, _Traits> &__os) {
    return __os.put(__os.widen('\t'));
  }
}

void test(string board)
{
    bool noThreat(TChessboard);
    TChessboard fillIt(string);
    void print(TChessboard);

    TChessboard r = fillIt(board);
    print(r);
    if (noThreat(r)) cout << tab << "CORRECT" << endl;
    else             cout << tab << "INCORRECT" << endl;
}

TChessboard fillIt(string s)
{
    TChessboard r;
    for (int i = 0; i < N; ++i)
        for (int j = 0; j < N; ++j)
            r[i][j] = s[i*N+j];
    return r;
}

void print(TChessboard m)
{
    cout << " ";
    for (int i = 0; i < N; ++i)
        cout << i;
    cout << endl;
    for (int i = 0; i < N; ++i) {
        cout << i;
        for (int j = 0; j < N; ++j)
            cout << m[i][j];
        cout << endl;
    }
}