Merge pull request #1627 from VaibhavArora314/patch

N Queens Solution

Program's_Contributed_By_Contributors/C++/NQueens.cpp

@@ -0,0 +1,70 @@
+#include <bits/stdc++.h>
+using namespace std;
+
+class Solution
+{
+    bool check(vector<string> curr, int curRow, int curCol)
+    {
+
+        for (int i = 0; i < curr.size(); i++)
+        {
+            if (curr[curRow][i] == 'Q')
+                return false;
+            if (curr[i][curCol] == 'Q')
+                return false;
+        }
+
+        int i = curRow, j = curCol;
+        while (i >= 0 && j >= 0)
+        {
+            if (curr[i][j] == 'Q')
+                return false;
+            i--;
+            j--;
+        }
+        i = curRow;
+        j = curCol;
+        while (i >= 0 && j < curr.size())
+        {
+            if (curr[i][j] == 'Q')
+                return false;
+            i--;
+            j++;
+        }
+        return true;
+    }
+    void helper(vector<string> curr, vector<vector<string>> &ans, int curRow)
+    {
+        if (curRow >= curr.size())
+        {
+            ans.push_back(curr);
+            return;
+        }
+
+        for (int i = 0; i < curr.size(); i++)
+        {
+            if (check(curr, curRow, i))
+            {
+                curr[curRow][i] = 'Q';
+                helper(curr, ans, curRow + 1);
+                curr[curRow][i] = '.';
+            }
+        }
+    }
+
+public:
+    vector<vector<string>> solveNQueens(int n)
+    {
+        vector<vector<string>> ans;
+
+        string str = "";
+        for (int i = 0; i < n; i++)
+        {
+            str += '.';
+        }
+
+        vector<string> temp(n, str);
+        helper(temp, ans, 0);
+        return ans;
+    }
+};