Merge pull request #3653 from NotADucc/0052

create 0052-n-queens-ii.cs

Author: Ykhan799

csharp/0052-n-queens-ii.cs

@@ -0,0 +1,48 @@
+public class Solution 
+{
+    public int TotalNQueens(int n) 
+    {
+        List<int> col = new List<int>(n);    
+        List<int> diag1 = new List<int>(n);  
+        List<int> diag2 = new List<int>(n);  
+        int output = 0;
+        Backtrack(ref output, col, diag1, diag2, n, 0, n);
+        return output;
+    }
+
+    private void Backtrack(ref int output, List<int> col, List<int> diag1, List<int> diag2, int grid_size, int row, int queens_left)
+    {
+        if(queens_left == 0)
+        {
+            output++;
+        }
+        else
+        {
+            for(int c = 0; c < grid_size; c++)
+            {
+                if(CanPlace(col, diag1, diag2, row, c))
+                {
+                    Place(col, diag1, diag2, row, c);
+                    Backtrack(ref output, col, diag1, diag2, grid_size, row + 1, queens_left - 1);
+                    Remove(col, diag1, diag2, row, c);
+                }
+            }
+        }
+    }
+    private bool CanPlace(List<int> col, List<int> diag1, List<int> diag2, int r, int c)
+    {
+        return !col.Contains(c) && !diag1.Contains(r + c) && !diag2.Contains(r - c);
+    }
+    private void Place(List<int> col, List<int> diag1, List<int> diag2, int r, int c)
+    {
+        col.Add(c);
+        diag1.Add(r + c);
+        diag2.Add(r - c);
+    }
+    private void Remove(List<int> col, List<int> diag1, List<int> diag2, int r, int c)
+    {
+        col.Remove(c);
+        diag1.Remove(r + c);
+        diag2.Remove(r - c);
+    }
+}