LeetCode算法笔记–Day34
21. Merge Two Sorted Lists
题目：
Merge two sorted linked lists and return it as a new sorted list. The new list should be made by splicing together the nodes of the first two lists.
example
input: 1->2->4, 1->3->4
output: 1->1->2->3->4->4
My Answer：
方法一：递归
- 时间复杂度：O(n + m)
- 空间复杂度：O(n + m)
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var mergeTwoLists = function(l1, l2) {
if (l1 === null) {
return l2;
} else if (l2 === null) {
return l1;
} else if (l1.val < l2.val) {
l1.next = mergeTwoLists(l1.next, l2);
return l1;
} else {
l2.next = mergeTwoLists(l1, l2.next);
return l2;
}
};
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方法二：迭代
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| /**
* Definition for singly-linked list.
* function ListNode(val, next) {
* this.val = (val===undefined ? 0 : val)
* this.next = (next===undefined ? null : next)
* }
*/
/**
* @param {ListNode} l1
* @param {ListNode} l2
* @return {ListNode}
*/
var mergeTwoLists = function(l1, l2) {
let preHead = new ListNode(-1);
let _pre = preHead;
while(l1 != null && l2 != null){
if(l1.val < l2.val){
_pre.next = l1;
l1 = l1.next;
}else{
_pre.next = l2;
l2 = l2.next;
}
_pre = _pre.next;
}
_pre.next = l1 == null ? l2 : l1;
return preHead.next
};
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