题目地址:
https://www.acwing.com/problem/content/34/
输入两个递增排序的链表,合并这两个链表并使新链表中的结点仍然是按照递增排序的。
二路归并。代码如下:
struct ListNode {
int val;
ListNode *next;
ListNode(int x): val(x) {
}
};
class Solution {
public:
ListNode* merge(ListNode* l1, ListNode* l2) {
ListNode *dummy = new ListNode(0), *prev = dummy;
while (l1 || l2) {
if (!l2) {
prev->next = l1;
l1 = l1->next;
prev = prev->next;
} else if (!l1) {
prev->next = l2;
l2 = l2->next;
prev = prev->next;
} else {
if (l1->val < l2->val) {
prev->next = l1;
l1 = l1->next;
} else {
prev->next = l2;
l2 = l2->next;
}
prev = prev->next;
}
}
return dummy->next;
}
};
时间复杂度 O ( l 1 + l 2 ) O(l_1+l_2) O(l1+l2),空间 O ( 1 ) O(1) O(1)。