Create 52. N-Queens II

Author: khushi3004

52. N-Queens II

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+class Solution {
+    int count;
+    public int totalNQueens(int n) {
+        count = 0;
+        List<int[]> queens = new ArrayList<>();
+        dfs(n, 0, queens);
+        return count;
+    }
+    
+    private void dfs(int n, int row, List<int[]> queens) {
+        if(queens.size() == n) {
+            count++;
+            return;
+        }
+        for(int col = 0; col < n; col++) {
+            if(canPlaceQueen(row, col, queens)) {
+                queens.add(new int[]{row, col});
+                dfs(n, row+1, queens);
+                queens.remove(queens.size()-1);
+            }
+        }
+    }
+    
+    private boolean canPlaceQueen(int row, int col, List<int[]> queens) {
+        for(int[] q : queens) {
+            int dx = Math.abs(q[0] - row);
+            int dy = Math.abs(q[1] - col);
+            if(dx == 0 || dy == 0 || dx == dy) return false;
+        }
+        return true;
+    }
+}