[leetcode]: 21. Merge Two Sorted Lists
1.题目
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.
合并两个有序的列表
2.分析
遍历两个列表,每次将较小的节点加入到合并列表的尾部。
3.代码
class Solution {
public:
//递归
ListNode* mergeTwoLists(ListNode* l1, ListNode* l2) {
if (l1 == NULL)
return l2;
if (l2 == NULL)
return l1;
ListNode* node = NULL;
if (l1->val < l2->val){
node = l1;
node->next = mergeTwoLists(l1->next, l2);
}
else {
node = l2;
node->next = mergeTwoLists(l1, l2->next);
}
return node;
}
//迭代
ListNode* mergeTwoLists(ListNode* l1, ListNode* l2) {
if (l1 == NULL)
return l2;
if (l2 == NULL)
return l1;
ListNode* head = new ListNode(0);
ListNode* tail = head;
while (l1&&l2) {
if (l1->val < l2->val){
tail->next = l1;
l1=l1->next;
}
else{
tail->next = l2;
l2=l2->next;
}
tail = tail->next;
}
tail->next = l1 ? l1 : l2;
return head->next;
}
};
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