21. Merge Two Sorted Lists

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.

分析:

就是使用两个指针，让较小的归并到新的list上：

代码：

方法一：

/**

* 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) {

ListNode tmp(INT_MIN);

ListNode * l3 = &tmp;

while(l1 && l2){

if(l1 -> val > l2 -> val){

l3 -> next = l2;

l2 = l2 -> next;

}

else{

l3 -> next = l1;

l1 = l1 -> next;

}

l3 = l3 -> next;

}

l3 -> next = l1 == NULL? l2 : l1;

return tmp.next;

}

};

方法二：递归

该方法并不是尾递归（tail-recursive）,所以当list过长，stack会溢出

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;

}

};

来源： http://tool.oschina.net/highlight

来自为知笔记(Wiz)

时间： 2024-12-15 06:59:31

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