链表 | LeetCode 21. 合并两个有序链表

21. 合并两个有序链表 - 力扣（LeetCode） (leetcode-cn.com)https://leetcode-cn.com/problems/merge-two-sorted-lists/

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public ListNode mergeTwoLists(ListNode list1, ListNode list2) {
        if (list1 == null)
            return list2;
        if (list2 == null)
            return list1;
        ListNode firstNode = new ListNode(0);
        ListNode p = firstNode;
        while (list1 != null && list2 != null) {
            if (list1.val < list2.val) {
                p.next = list1;
                list1 = list1.next;
            }else {
                p.next = list2;
                list2 = list2.next;
            }
            p = p.next;
        }
        if (list1 != null) {
            p.next = list1;
        }
        if (list2 != null) {
            p.next = list2;
        }
        return firstNode.next;
    }
}

循环+双指针，遍历所有节点同时比较大小连接起来即可。