leetcode [Merge Two Sorted Lists]

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/** * Definition for singly-linked list. * public class ListNode { *     int val; *     ListNode next; *     ListNode(int x) { val = x; } * } */public class Solution {    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {        ListNode res = new ListNode(0);        ListNode temp = res;//记得右移一位        while(l1 != null && l2 != null){        if(l1.val <= l2.val){        temp.next = new ListNode(l1.val);        temp = temp.next;        l1 = l1.next;        }        else{        temp.next = new ListNode(l2.val);        temp = temp.next;        l2 = l2.next;        }        }        while(l1 != null){        temp.next = new ListNode(l1.val);        temp = temp.next;        l1 = l1.next;        }        while(l2 != null){        temp.next = new ListNode(l2.val);        temp = temp.next;        l2 = l2.next;        }        res = res.next;        return res;    }}

解法二（递归）：

/** * Definition for singly-linked list. * public class ListNode { *     int val; *     ListNode next; *     ListNode(int x) { val = x; } * } */public class Solution {    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {//递归求法    ListNode res = null;    if(l1 == null){return l2;}//递归出口    if(l2 == null){return l1;}//递归出口    if(l1.val <= l2.val){    res = new ListNode(l1.val);    res.next = mergeTwoLists(l1.next, l2);    }    else{    res = new ListNode(l2.val);    res.next = mergeTwoLists(l1, l2.next);    }        return res;    }}

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