21. Merge Two Sorted Lists
比以前强很多了O(∩_∩)O
解析
solution:迭代
class Solution {
public:
ListNode* mergeTwoLists(ListNode* l1, ListNode* l2) {
ListNode dummy(-1);
ListNode* walk = &dummy;
while(l1 !=NULL && l2 !=NULL){
int val1 = l1->val;
int val2 = l2->val;
if(val1<val2){
walk->next = l1;
l1 = l1->next;
}
else{
walk->next = l2;
l2 = l2->next;
}
walk = walk->next;
}
if(l1 != NULL)
walk->next = l1;
if(l2 != NULL)
walk->next = l2;
return dummy.next;
}
};
solution:大佬的递归:
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;
}
}
};