Merge pull request #30 from jpriyanshu1406/leetpj

Solutions for N QUEENS Priyanshu Jaiswal

Author: kishanrajput23

N QUEENS

@@ -0,0 +1,29 @@
+class Solution {
+ public:
+  vector<vector<string>> solveNQueens(int n) {
+    vector<vector<string>> ans;
+    dfs(n, 0, vector<bool>(n), vector<bool>(2 * n - 1), vector<bool>(2 * n - 1),
+        vector<string>(n, string(n, '.')), ans);
+    return ans;
+  }
+
+ private:
+  void dfs(int n, int i, vector<bool>&& cols, vector<bool>&& diag1,
+           vector<bool>&& diag2, vector<string>&& board,
+           vector<vector<string>>& ans) {
+    if (i == n) {
+      ans.push_back(board);
+      return;
+    }
+
+    for (int j = 0; j < n; ++j) {
+      if (cols[j] || diag1[i + j] || diag2[j - i + n - 1])
+        continue;
+      board[i][j] = 'Q';
+      cols[j] = diag1[i + j] = diag2[j - i + n - 1] = true;
+      dfs(n, i + 1, move(cols), move(diag1), move(diag2), move(board), ans);
+      cols[j] = diag1[i + j] = diag2[j - i + n - 1] = false;
+      board[i][j] = '.';
+    }
+  }
+};