Create n-queens.cpp

Author: rishi058

C++/n-queens.cpp

@@ -0,0 +1,90 @@
+#include <bits/stdc++.h>
+using namespace std;
+
+int n;
+vector<vector<int>> board;
+vector<vector<vector<int>>> v;
+
+/*
+Give input n = no. of queens...
+Output --> All Combinations of positions of n queens so that no queen can attack other..
+*/
+
+bool is_safe(int row, int col){
+
+    int x = row, y = col;
+    //check for same row
+    while(y>=0){
+        if(board[x][y]==1){return false;}
+        y--;
+    }
+
+    int xx = row, yy = col;
+    //check for diagonal
+    while(xx>=0 && yy>=0){
+        if(board[xx][yy]==1){return false;}
+        xx--; yy--;
+    }
+
+    int a = row, b = col;
+    //check for diagonal
+    while(a<n && b>=0){
+        if(board[a][b]==1){return false;}
+        a++; b--;
+    }
+
+    return true;
+
+}
+
+
+
+void solve(int col, int n){
+
+    // base case (if every col is filled)
+    if(col == n){
+        v.push_back(board);
+        return;
+    }
+
+    //put queen in every row of diff col..
+    for(int row = 0; row<n; row++){
+        if(is_safe(row,col)){
+
+            // if placing queen is safe
+            board[row][col] = 1;
+
+            solve(col+1, n);
+
+            //backtrack
+            board[row][col] = 0;
+        }
+    }
+
+
+}
+
+int main()
+{
+    cin>>n;
+
+    for(int i=0; i<n; i++){
+        vector<int> temp(n, 0);
+        board.push_back(temp);
+    }
+
+    solve(0, n);
+    cout<<v.size()<<"\n";
+
+    for(auto b : v){
+        for(auto vv : b){
+            for(int g : vv){
+                cout<<g<<" ";
+            }
+            cout<<"\n";
+        }
+        cout<<"\n\n";
+    }
+
+
+}