DSA_Busted_Sheet/nQueenProblem.cpp at main · Santosh-Pathak/DSA_Busted_Sheet · GitHub

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#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
void printSolution(vector<vector<char>> board, int n)
{
    for (int i = 0; i < n; i++)
    {
        for (int j = 0; j < n; j++)
        {
            cout << board[i][j] << " ";
        }
        cout << endl;
    }
    cout << endl
         << endl;
}
bool isSafe(int row, int col, vector<vector<char>> &board, int n)
{
    // check karna chahte h , k kya main
    // current cell [row,col] pr QUEEN rakh
    // sakta hu ya nahi
    int i = row;
    int j = col;

    // check row
    while (j >= 0)
    {
        if (board[i][j] == 'Q')
        {
            return false;
        }
        j--;
    }

    // check upper left diaglnol
    i = row;
    j = col;
    while (i >= 0 && j >= 0)
    {
        if (board[i][j] == 'Q')
        {
            return false;
        }
        i--;
        j--;
    }

    // check bottom left diagnol
    i = row;
    j = col;
    while (i < n && j >= 0)
    {
        if (board[i][j] == 'Q')
        {
            return false;
        }
        i++;
        j--;
    }

    // kahin pr bhi queen nahi mili
    // iska matlab ye position safe hai
    // iska matlab eturn kardo true
    return true;
}

void solve(vector<vector<char>> &board, int col, int n)
{
    // base case
    if (col >= n)
    {
        printSolution(board, n);
        return;
    }

    // 1 case solve karna h , bakki recursion sambhal lega
    for (int row = 0; row < n; row++)
    {
        if (isSafe(row, col, board, n))
        {
            board[row][col] = 'Q';
            // recursion
            solve(board, col + 1, n);
            // backtraking
            board[row][col] = '-';
        }
    }
}
int main()
{
    int n = 6;
    vector<vector<char>> board(n, vector<char>(n, '-'));
    int col = 0;

    // - => empty cell
    // 'Q' => Queen at the cell

    solve(board, col, n);
    return 0;
}

// // OPTIMISED SOLUTION
// class Solution {
// public:

//     unordered_map<int,bool> rowCheck;
//     unordered_map<int,bool> upperLeftDiagnolCheck;
//     unordered_map<int,bool> bottomLeftDiagnolCheck;

//     void storeSolution(vector<vector<char>> &board, int n, vector<vector<string> > &ans) {
//         vector<string> temp;
//         for(int i=0; i<n; i++) {
//             string output = "";
//             for(int j=0; j<n ;j++) {
//                 output.push_back(board[i][j]);
//             }
//             temp.push_back(output);
//         }
//         ans.push_back(temp);
//     }


//     bool isSafe(int row, int col, vector<vector<char>> &board, int n) {

//         if(rowCheck[row] == true )
//             return false;

//         if(upperLeftDiagnolCheck[n-1+col-row] == true)
//             return false;

//         if(bottomLeftDiagnolCheck[row+col] == true)
//             return false;

//         return true;

// }


//     void solve(vector<vector<char>> &board, int col, int n, vector<vector<string> > &ans  ) {
//     //base case
//     if(col >= n) {
//         storeSolution(board, n, ans);
//         return ;
//     }

//     //1 case solve karna h , baaki recursion sambhal lega

//     for(int row = 0; row <n; row++) {
//         if(isSafe(row, col, board, n)) {
//         //rakh do
//         board[row][col] = 'Q';
//         rowCheck[row] = true;
//         upperLeftDiagnolCheck[n-1+col-row] = true;
//         bottomLeftDiagnolCheck[row+col] = true;

//         //recursion solution laega
//         solve(board, col+1, n, ans);
//         //backtracking
//         board[row][col] = '.';
//         rowCheck[row] = false;
//         upperLeftDiagnolCheck[n-1+col-row] = false;
//         bottomLeftDiagnolCheck[row+col] = false;
//         }

//     }
// }


//     vector<vector<string>> solveNQueens(int n) {
//         vector<vector<char>> board(n, vector<char>(n,'.'));
//         vector<vector<string> > ans;
//         int col = 0;
//         //0 -> empty cell
//         //1 -> Queen at the cell
//         solve(board, col, n, ans);
//         return ans;
//     }
// };