https://leetcode-cn.com/problems/merge-two-sorted-lists/
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:
输入:1->2->4, 1->3->4
输出:1->1->2->3->4->4
解法1
递归。8ms, 7.1mb
/**
* 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 (l1 == nullptr) {
return l2;
}
if (l2 == nullptr) {
return l1;
}
if (l1->val <= l2->val) {
l1->next = mergeTwoLists(l1->next, l2);
return l1;
} else {
l2->next = mergeTwoLists(l1, l2->next);
return l2;
}
}
};
解法2
迭代。20 ms 7 MB
class Solution {
public:
ListNode* mergeTwoLists(ListNode* l1, ListNode* l2) {
ListNode* res = new ListNode(-1);
ListNode* p = res;
while (l1 != nullptr && l2 != nullptr) {
if (l1->val <= l2->val) {
p->next = l1;
l1 = l1->next;
} else {
p->next = l2;
l2 = l2->next;
}
p = p->next;
}
p->next = l1 == nullptr ? l2 : l1;
return res->next;
}
};
EOF