commit

Author: 王俊超

.idea/modules.xml

@@ -0,0 +1,63 @@
+import java.util.Arrays;
+
+/**
+ * @author: wangjunchao(王俊超)
+ * @time: 2018-09-28 15:38
+ **/
+public class Solution {
+    public int totalNQueens(int n) {
+        int[] result = {0};
+
+        if (n < 1) {
+            return result[0];
+        }
+
+        char[][] board = new char[n][];
+        for (int i = 0; i < n; i++) {
+            board[i] = new char[n];
+            Arrays.fill(board[i], '.');
+        }
+
+        solveNQueens(board, 0, result);
+        return result[0];
+    }
+
+    private void solveNQueens(char[][] board, int row, int[] result) {
+        if (board.length == row) {
+            result[0]++;
+        }
+
+        for (int col = 0; col < board.length; col++) {
+            if (canPlace(board, row, col)) {
+                board[row][col] = 'Q';
+                solveNQueens(board, row + 1, result);
+                board[row][col] = '.';
+            }
+        }
+    }
+
+    private boolean canPlace(char[][] board, int row, int col) {
+        // 检测之前的列上是否已经放过皇后
+        for (int i = 0; i < row; ++i) {
+            if (board[i][col] == 'Q') {
+                return false;
+            }
+        }
+
+        // 45度角(左下角)上是否已经存在过皇后
+        for (int i = row - 1, j = col - 1; i >= 0 && j >= 0; --i, --j) {
+            if (board[i][j] == 'Q') {
+                return false;
+            }
+        }
+
+        // 135度角上（左上角）是否已经存在过皇后
+        for (int i = row - 1, j = col + 1; i >= 0 && j < board.length; --i, ++j) {
+            if (board[i][j] == 'Q') {
+                return false;
+            }
+        }
+
+        return true;
+    }
+}