20231221 Finished

src/solution/mod.rs

@@ -6,3 +6,4 @@ mod s0002_add_two_numbers;
 mod s0003_longest_substring_without_repeating_characters;
 mod s0162_find_peak_element;
 mod s2828_check_if_a_string_is_an_acronym_of_words;
+mod s0052_n_queens_ii;

src/solution/s0052_n_queens_ii.rs

@@ -0,0 +1,89 @@
+/**
+ * [52] N-Queens II
+ *
+ * The n-queens puzzle is the problem of placing n queens on an n x n chessboard such that no two queens attack each other.
+ * Given an integer n, return the number of distinct solutions to the n-queens puzzle.
+ *  
+ * <strong class="example">Example 1:
+ * <img alt="" src="https://assets.leetcode.com/uploads/2020/11/13/queens.jpg" style="width: 600px; height: 268px;" />
+ * Input: n = 4
+ * Output: 2
+ * Explanation: There are two distinct solutions to the 4-queens puzzle as shown.
+ * 
+ * <strong class="example">Example 2:
+ * 
+ * Input: n = 1
+ * Output: 1
+ * 
+ *  
+ * Constraints:
+ * 
+ * 	1 <= n <= 9
+ * 
+ */
+pub struct Solution {}
+
+// problem: https://leetcode.cn/problems/n-queens-ii/
+// discuss: https://leetcode.cn/problems/n-queens-ii/discuss/?currentPage=1&orderBy=most_votes&query=
+
+// submission codes start here
+
+use std::collections::VecDeque;
+
+impl Solution {
+    pub fn total_n_queens(n: i32) -> i32 {
+        let n = n as usize;
+        let mut result = 0;
+        let mut stack = VecDeque::new();
+
+        for i in 0..n {
+            stack.push_back((0usize, i, false));
+        }
+
+        let mut x_occupied = vec![false; n];
+        let mut y_occupied = vec![false; 2 * n - 1];
+        let mut z_occupied = vec![false; 2 * n - 1];
+
+        while let Some((x, y, flag)) = stack.pop_back() {
+            if flag {
+                x_occupied[y] = false;
+                y_occupied[n -  1 + x - y] = false;
+                z_occupied[x + y] = false;
+            } else {
+                x_occupied[y] = true;
+                y_occupied[n -  1 + x - y] = true;
+                z_occupied[x + y] = true;
+
+                stack.push_back((x, y, true));
+
+                if x == n - 1 {
+                    result += 1;
+                    continue;
+                }
+
+                for j in 0..n {
+                    // 注意这里在判断的点是(x + 1, j)
+                    if !x_occupied[j] && !y_occupied[n + x - j] && !z_occupied[x + 1 + j] {
+                        stack.push_back((x + 1, j, false));
+                    }
+                }
+            }
+        }
+
+        result
+    }
+}
+
+// submission codes end
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_52() {
+        assert_eq!(1, Solution::total_n_queens(1));
+        assert_eq!(2, Solution::total_n_queens(4));
+        assert_eq!(14200, Solution::total_n_queens(12));
+    }
+}

src/solution/s0162_find_peak_element.rs

@@ -34,7 +34,7 @@ pub struct Solution {}
 impl Solution {
     pub fn find_peak_element(nums: Vec<i32>) -> i32 {
         if nums.len() == 1 {
-            0
+            return 0;
         }
 
         let (mut left, mut right) = (0, nums.len() - 1);