From 7a429700ae1bc4b5f99f0ee8fd9b510d5f13d9ba Mon Sep 17 00:00:00 2001
From: ckl <1051928078@qq.com>
Date: Mon, 17 Oct 2022 20:16:55 +0800
Subject: [PATCH] =?UTF-8?q?=E6=B7=BB=E5=8A=A0=200052.N=E7=9A=87=E5=90=8EII?=
 =?UTF-8?q?.md=20Java=E7=89=88=E6=9C=AC?=
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---
 problems/0052.N皇后II.md | 49 +++++++++++++++++++++++++++++++++++++-
 1 file changed, 48 insertions(+), 1 deletion(-)

diff --git a/problems/0052.N皇后II.md b/problems/0052.N皇后II.md
index f1edd281..e4faac0c 100644
--- a/problems/0052.N皇后II.md
+++ b/problems/0052.N皇后II.md
@@ -256,7 +256,54 @@ int totalNQueens(int n){
     return answer;
 }
 ```
-
+Java
+```java
+class Solution {
+    int count = 0;
+    public int totalNQueens(int n) {
+        char[][] board = new char[n][n];
+        for (char[] chars : board) {
+            Arrays.fill(chars, '.');
+        }
+        backTrack(n, 0, board);
+        return count;
+    }
+    private void backTrack(int n, int row, char[][] board) {
+        if (row == n) {
+            count++;
+            return;
+        }
+        for (int col = 0; col < n; col++) {
+            if (isValid(row, col, n, board)) {
+                board[row][col] = 'Q';
+                backTrack(n, row + 1, board);
+                board[row][col] = '.';
+            }
+        }
+    }
+    private boolean isValid(int row, int col, int n, char[][] board) {
+        // 检查列
+        for (int i = 0; i < row; ++i) {
+            if (board[i][col] == 'Q') {
+                return false;
+            }
+        }
+        // 检查45度对角线
+        for (int i = row - 1, j = col - 1; i >= 0 && j >= 0; i--, j--) {
+            if (board[i][j] == 'Q') {
+                return false;
+            }
+        }
+        // 检查135度对角线
+        for (int i = row - 1, j = col + 1; i >= 0 && j <= n - 1; i--, j++) {
+            if (board[i][j] == 'Q') {
+                return false;
+            }
+        }
+        return true;
+    }
+}
+```
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