solve 19

Author: Zhang Xiaodong

src/solution/mod.rs

@@ -14,3 +14,4 @@ mod s0015_3sum;
 mod s0016_3sum_closest;
 mod s0017_letter_combinations_of_a_phone_number;
 mod s0018_4sum;
+mod s0019_remove_nth_node_from_end_of_list;

src/solution/s0019_remove_nth_node_from_end_of_list.rs

@@ -0,0 +1,95 @@
+/**
+ * [19] 删除链表的倒数第 N 个结点
+ *
+ * 给你一个链表，删除链表的倒数第 n 个结点，并且返回链表的头结点。
+ *  
+ * 示例 1：
+ * <img alt="" src="https://assets.leetcode.com/uploads/2020/10/03/remove_ex1.jpg" style="width: 542px; height: 222px;" />
+ * 输入：head = [1,2,3,4,5], n = 2
+ * 输出：[1,2,3,5]
+ * 
+ * 示例 2：
+ * 
+ * 输入：head = [1], n = 1
+ * 输出：[]
+ * 
+ * 示例 3：
+ * 
+ * 输入：head = [1,2], n = 1
+ * 输出：[1]
+ * 
+ *  
+ * 提示：
+ * 
+ * 	链表中结点的数目为 sz
+ * 	1 <= sz <= 30
+ * 	0 <= Node.val <= 100
+ * 	1 <= n <= sz
+ * 
+ *  
+ * 进阶：你能尝试使用一趟扫描实现吗？
+ * 
+ */
+pub struct Solution {}
+use std::borrow::BorrowMut;
+
+use crate::util::linked_list::{ListNode, to_list};
+
+// problem: https://leetcode.cn/problems/remove-nth-node-from-end-of-list/
+// discuss: https://leetcode.cn/problems/remove-nth-node-from-end-of-list/discuss/?currentPage=1&orderBy=most_votes&query=
+
+// submission codes start here
+
+// Definition for singly-linked list.
+// #[derive(PartialEq, Eq, Clone, Debug)]
+// pub struct ListNode {
+//   pub val: i32,
+//   pub next: Option<Box<ListNode>>
+// }
+//
+// impl ListNode {
+//   #[inline]
+//   fn new(val: i32) -> Self {
+//     ListNode {
+//       next: None,
+//       val
+//     }
+//   }
+// }
+impl Solution {
+    pub fn remove_nth_from_end(head: Option<Box<ListNode>>, n: i32) -> Option<Box<ListNode>> {
+        let mut dummy_head = Box::new(ListNode {
+            next: head,
+            val: 0,
+        });
+        unsafe {
+            let mut slow = &mut dummy_head as *mut Box<ListNode>;
+            let mut fast = &mut dummy_head as *mut Box<ListNode>;
+            for _ in 0..n {
+                fast = (*fast).next.as_mut().unwrap();
+            }
+            while (*fast).next.is_some() {
+                fast = (*fast).next.as_mut().unwrap();
+                slow = (*slow).next.as_mut().unwrap();
+            }
+            (*slow).next = (*slow).next.take().unwrap().next;
+        }
+        dummy_head.next
+    }
+}
+
+// submission codes end
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_19() {
+        assert_eq!(
+            Solution::remove_nth_from_end(to_list(vec![1, 2, 3, 4, 5]), 2),
+            to_list(vec![1, 2, 3, 5])
+        );
+        assert_eq!(Solution::remove_nth_from_end(to_list(vec![1]), 1), None);
+    }
+}