solve 21

Author: Zhang Xiaodong

src/solution/mod.rs

@@ -16,3 +16,4 @@ mod s0017_letter_combinations_of_a_phone_number;
 mod s0018_4sum;
 mod s0019_remove_nth_node_from_end_of_list;
 mod s0020_valid_parentheses;
+mod s0021_merge_two_sorted_lists;

src/solution/s0021_merge_two_sorted_lists.rs

@@ -0,0 +1,101 @@
+/**
+ * [21] 合并两个有序链表
+ *
+ * 将两个升序链表合并为一个新的 升序 链表并返回。新链表是通过拼接给定的两个链表的所有节点组成的。 
+ *  
+ * 示例 1：
+ * <img alt="" src="https://assets.leetcode.com/uploads/2020/10/03/merge_ex1.jpg" style="width: 662px; height: 302px;" />
+ * 输入：l1 = [1,2,4], l2 = [1,3,4]
+ * 输出：[1,1,2,3,4,4]
+ * 
+ * 示例 2：
+ * 
+ * 输入：l1 = [], l2 = []
+ * 输出：[]
+ * 
+ * 示例 3：
+ * 
+ * 输入：l1 = [], l2 = [0]
+ * 输出：[0]
+ * 
+ *  
+ * 提示：
+ * 
+ * 	两个链表的节点数目范围是 [0, 50]
+ * 	-100 <= Node.val <= 100
+ * 	l1 和 l2 均按 非递减顺序 排列
+ * 
+ */
+pub struct Solution {}
+use crate::util::linked_list::{ListNode, to_list};
+
+// problem: https://leetcode.cn/problems/merge-two-sorted-lists/
+// discuss: https://leetcode.cn/problems/merge-two-sorted-lists/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 merge_two_lists(list1: Option<Box<ListNode>>, list2: Option<Box<ListNode>>) -> Option<Box<ListNode>> {
+        let mut dummy_head = Some(Box::new(ListNode {
+            val: 0,
+            next: None,
+        }));
+        let mut p = &mut dummy_head;
+        let mut p1 = list1;
+        let mut p2 = list2;
+        while p1.is_some() || p2.is_some() {
+            if p1.is_none() {
+                p.as_mut().unwrap().next = p2;
+                break;
+            } else if p2.is_none() {
+                p.as_mut().unwrap().next = p1;
+                break;
+            }
+            let next = if p1.as_ref().unwrap().val > p2.as_ref().unwrap().val {
+                let n = p2.as_mut().unwrap().next.take();
+                let next = p2.take();
+                p2 = n;
+                next
+            } else {
+                let n = p1.as_mut().unwrap().next.take();
+                let next = p1.take();
+                p1 = n;
+                next
+            };
+            p.as_mut().unwrap().next = next;
+            p = &mut p.as_mut().unwrap().next;
+        }
+        dummy_head.unwrap().next
+    }
+}
+
+// submission codes end
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_21() {
+        assert_eq!(
+            Solution::merge_two_lists(to_list(vec![1, 2, 4]), to_list(vec![1, 3, 4])),
+            to_list(vec![1, 1, 2, 3, 4, 4])
+        );
+    }
+}