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algorithm notes: leetcode#21 merge two sorted lists

admin 11月 12, 2020 0

Problem

Solution

Initial thoughts

Python implementation

# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None
class :
    def mergeTwoLists(self, l1, l2):
        """
        :type l1: ListNode
        :type l2: ListNode
        :rtype: ListNode
        """
        if l1 is None:
            return l2
        if l2 is None:
            return l1
        if l1.val < l2.val:
            l1.next = self.mergeTwoLists(l1.next, l2)
            return l1
        else:
            l2.next = self.mergeTwoLists(l1, l2.next)
            return l2

Java implementation

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class  {
    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
        if(l1 == null){ return l2; }
        if(l2 == null){ return l1; }
        if(l1.val < l2.val){
            l1.next = mergeTwoLists(l1.next, l2);
            return l1;
        }else{
            l2.next = mergeTwoLists(l1, l2.next);
            return l2;
        }
    }
}

Time complexity

O(m+n).

Space complexity

O(m+n).

Links

21. Merge Two Sorted Lists
(中文版) 算法笔记: 力扣#21 合并两个有序链表