leetcode 21 Merge Two Sorted Lists

Merge two sorted linked lists and return it as a new list. The new list should be made by splicing together the nodes of the first two lists.

我的解决方式：

/*** Definition for singly-linked list.* struct ListNode {*     int val;*     ListNode *next;*     ListNode(int x) : val(x), next(NULL) {}* };*/class Solution
{
public:ListNode* mergeTwoLists(ListNode* l1, ListNode* l2) {if(NULL==l1) return l2;if(NULL==l2) return l1;ListNode* head = NULL;if(l1->val < l2->val)     {head = l1; l1 = l1->next; }else                       { head = l2; l2 = l2->next;}ListNode* p = head;     // pointer to form new listwhile(l1!=NULL&&l2!=NULL){if(l1->val < l2->val){p->next = l1;l1 = l1 ->next;}else {p->next = l2;l2 = l2 ->next;}p = p->next;}if(l1){p->next = l1;}else{p->next = l2;}return head;}
};

递归c++解法：

class Solution {
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(l2->next, l1);return l2;}}
};

python递归解决方式：

def mergeTwoLists(self, l1, l2):if not l1:return l2elif not l2:return l1else:if l1.val <= l2.val:l1.next = self.mergeTwoLists(l1.next, l2)return l1else:l2.next = self.mergeTwoLists(l1, l2.next)return l2

python非递归：

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = Noneclass Solution:# @param {ListNode} l1# @param {ListNode} l2# @return {ListNode}def mergeTwoLists(self, l1, l2):p1 = l1p2 = l2guard = ListNode(0)q = guardwhile p1 is not None and p2 is not None:if p1.val <= p2.val:q.next = p1p1 = p1.nextq = q.nextelse:q.next = p2p2 = p2.nextq = q.nextif p1 is not None:q.next = p1if p2 is not None:q.next = p2return guard.next

python递归解决方式2：

If both lists are non-empty, I first make sure a starts smaller, use its head as result, and merge the remainders behind it. Otherwise, i.e., if one or both are empty, I just return what's there.class Solution:def mergeTwoLists(self, a, b):if a and b:if a.val > b.val:a, b = b, aa.next = self.mergeTwoLists(a.next, b)return a or b

转载于:https://www.cnblogs.com/mfrbuaa/p/5371604.html

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