20241201 finished.

src/problem/mod.rs

@@ -344,3 +344,5 @@ mod p3208_alternating_groups_ii;
 mod p3250_find_the_count_of_monotonic_pairs_i;
 
 mod p3232_find_if_digit_game_can_be_won;
+
+mod p51_n_queens;

src/problem/p51_n_queens.rs

@@ -0,0 +1,67 @@
+/**
+ * [51] N-Queens
+ */
+pub struct Solution {}
+
+// submission codes start here
+
+impl Solution {
+    pub fn solve_n_queens(n: i32) -> Vec<Vec<String>> {
+        let n = n as usize;
+
+        let mut chessboard = Vec::with_capacity(n);
+        let mut result = vec![];
+
+        Self::dfs(0, n, &mut chessboard, &mut result);
+
+        result
+    }
+
+    fn dfs(y: usize, n: usize, chessboard: &mut Vec<usize>, result: &mut Vec<Vec<String>>) {
+        if y == n {
+            result.push(
+                chessboard
+                    .iter()
+                    .map(|&x| {
+                        let mut row = vec!['.'; n];
+                        row[x] = 'Q';
+
+                        row.into_iter().collect()
+                    })
+                    .collect(),
+            );
+            return;
+        }
+
+        for x in 0..n {
+            if chessboard.iter().any(|&dx| dx == x) {
+                continue;
+            }
+
+            if chessboard
+                .iter()
+                .enumerate()
+                .any(|(dy, &dx)| x.abs_diff(dx) == y.abs_diff(dy))
+            {
+                continue;
+            }
+
+            chessboard.push(x);
+            Self::dfs(y + 1, n, chessboard, result);
+            chessboard.pop();
+        }
+    }
+}
+
+// submission codes end
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_51() {
+        assert_eq!(2, Solution::solve_n_queens(4).len());
+        assert_eq!(vec![vec_string!("Q")], Solution::solve_n_queens(1));
+    }
+}