merge two sorted linked list with duplicates

原创于 2012-06-01 09:26:22 发布 · 677 阅读

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文章标签：

#duplicates #list #merge #null #pointers

链表（linkedlist）专栏收录该内容

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本文介绍了一种在常数空间复杂度下合并两个已排序链表的方法。通过比较两个链表节点的值，将较小值节点连接到结果链表中，直至其中一个链表遍历完成。最后将未结束的链表剩余部分直接连接到结果链表末尾。

Question:

Given two sorted linked list, and merge them without using extra space (using constant space is allowed). For example, if 1 -> 2 -> 5 merges with 2 -> 4 -> 5, we have 1 -> 2 -> 4 -> 5

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */
public class Solution {
    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
        if (l1 == null ) return l2;
        if (l2 == null ) return l1;
        ListNode head = null;
        ListNode current = null;
        if (l1.val <= l2.val) {
            head = l1;
            l1 = l1.next;
        } else {
            head = l2;
            l2 = l2.next;
        }
        current = head;
        
        while (l1 != null && l2 != null) {
            if (l1.val < l2.val) {
                current.next = l1;
                l1 = l1.next;
            } else {
                current.next = l2;
                l2 = l2.next;
            }
            current = current.next;
        }
        
        if (l1 != null) current.next = l1;
        if (l2 != null) current.next = l2; 
        return head;
    }
}

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