nqueens solver i wound up writing on the side while guiding someone thoruhg c multidimensional arrays

nqueens.cpp

#include <vector>
#include <algorithm>
#include <numeric>
#include <set>
#include <iterator>
#include <iostream>

bool is_nqueens(const std::vector<int>& pos) {
    //assume row and col safety
    std::set<int> diag1;
    std::set<int> diag2;
    for(int i = 0; i < pos.size(); ++i) {
        diag1.insert(pos[i]-i);
        diag2.insert(pos[i]+i);
    }
    return (diag1.size() == pos.size()) && (diag2.size() == pos.size());
}

void print(const std::vector<int>& pos) {
    for(int i = 0; i < pos.size(); ++i) {
        for(int j = 0; j < pos[i]; ++j) {
            std::cout << ".";
        }
        std::cout << "o";
        for(int j = pos[i]+1; j < pos.size(); ++j) {
            std::cout << ".";
        }
        std::cout << std::endl;
    }
    for(int j = 0; j < pos.size(); ++j) {
        std::cout << "=";
    }
    std::cout << std::endl;
}

int main(int argc, char * argv[]) {
    int size = 8;
    if(argc == 2) {
        size = std::atoi(argv[1]);
    }

    std::vector<int> pos(size);
    std::iota(pos.begin(),pos.end(),0);
    do {
        if(is_nqueens(pos)) {
            print(pos);
        }
        std::next_permutation(pos.begin(),pos.end());

    } while(!std::is_sorted(pos.begin(),pos.end()));
    return 0;
}