2024/9/13 Hot100 回溯 最后一题n皇后，昨日

src/main/java/com/cool/hot100/backtracking/Num51.java

@@ -0,0 +1,65 @@
+package com.cool.hot100.backtracking;
+
+import org.junit.Test;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+/**
+ * Created with IntelliJ IDEA.
+ *
+ * @Author: Cool
+ * @Date: 2024/09/13/09:50
+ * DayNumber 1
+ * Hard 3
+ * Level 6
+ */
+public class Num51 {
+
+    char[][] chars;
+    boolean[] xBool;
+    boolean[] dir1;
+    boolean[] dir2;
+    int n;
+    List<List<String>> res = new ArrayList<>();
+
+    public List<List<String>> solveNQueens(int n) {
+        this.n = n;
+        chars = new char[n][n];
+        xBool = new boolean[n];
+        dir1 = new boolean[2 * n];
+        dir2 = new boolean[2 * n];
+        for (int i = 0; i < n; i++) {
+            Arrays.fill(chars[i], '.');
+        }
+        dfs(0);
+        return res;
+    }
+
+    private void dfs(int y) {
+        if (y >= n) {
+            List<String> list = new ArrayList<>();
+            for (char[] cs : chars) {
+                list.add(new String(cs));
+            }
+            res.add(list);
+            return;
+        }
+        for (int x = 0; x < n; x++) {
+            if (xBool[x] || dir1[x + y] || dir2[x - y + n]) {
+                continue;
+            }
+            xBool[x] = dir1[x + y] = dir2[x - y + n] = true;
+            chars[x][y] = 'Q';
+            dfs(y + 1);
+            xBool[x] = dir1[x + y] = dir2[x - y + n] = false;
+            chars[x][y] = '.';
+        }
+    }
+
+    @Test
+    public void test() {
+        solveNQueens(4);
+    }
+}