[Leetcode]_21 Merge Two Sorted Lists

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/** *  Index: 21 *  Title: Merge Two Sorted Lists *  Author: ltree98 **/

将两个有序的数组合并成一个数组。

第三方介入

最通俗易懂的，设置一个第三方，来进行存储合并。

/** * 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* l3 = new ListNode(0);        ListNode* head = l3;        while(l1 && l2) {            if(l1->val <= l2->val)  {                ListNode* temp = new ListNode(l1->val);                l3->next = temp;                l1 = l1->next;            }            else    {                ListNode* temp = new ListNode(l2->val);                l3->next = temp;                l2 = l2->next;            }            l3 = l3->next;        }        if(l1)            l3->next = l1;        else            l3->next = l2;        return head->next;    }};

递归

/** * 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) {        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(l1, l2->next);            return l2;        }    }};

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