Create main.cpp

Author: JawadSher

20 - Hashmap Data Structure Problems/03 - N - Queens/main.cpp

@@ -0,0 +1,50 @@
+class Solution {
+    public:
+
+        void addSolution(vector<vector<string>>& ans, vector<int>& board, int n){
+            vector<string> temp;
+
+            for(int i = 0; i < n; i++){
+                string row(n, '.');
+                row[board[i]] = 'Q';
+                temp.push_back(row);
+            }
+            ans.push_back(temp);
+        }
+
+        void solve(int col, vector<vector<string>>& ans, vector<int>& board, unordered_set<int>& rows, unordered_set<int>& primaryDiag, unordered_set<int>& secondaryDiag, int n){
+            if(col == n){
+                addSolution(ans, board, n);
+                return;
+            }
+
+            for(int row = 0; row < n; row++){
+                int diag1 = row - col;
+                int diag2 = row + col;
+
+                if(rows.find(row) == rows.end() && primaryDiag.find(diag1) == primaryDiag.end() && secondaryDiag.find(diag2) == secondaryDiag.end()){
+                    board[col] = row;
+                    rows.insert(row);
+                    primaryDiag.insert(diag1);
+                    secondaryDiag.insert(diag2);
+
+                    solve(col + 1, ans, board, rows, primaryDiag, secondaryDiag, n);
+
+                    board[col] = -1;
+                    rows.erase(row);
+                    primaryDiag.erase(diag1);
+                    secondaryDiag.erase(diag2);
+                }
+            }
+        }
+        vector<vector<string>> solveNQueens(int n) {
+            vector<int> board(n, -1);
+            vector<vector<string>> ans;
+            unordered_set<int> rows;
+            unordered_set<int> primaryDaig;
+            unordered_set<int> secondaryDaig;
+
+            solve(0, ans, board, rows, primaryDaig, secondaryDaig, n);
+            return ans;
+        }
+};