题解 | 合并两个排序的链表

import java.util.*;

/*
 * public class ListNode {
 *   int val;
 *   ListNode next = null;
 *   public ListNode(int val) {
 *     this.val = val;
 *   }
 * }
 */

public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     *
     * @param pHead1 ListNode类
     * @param pHead2 ListNode类
     * @return ListNode类
     */
    public ListNode Merge (ListNode pHead1, ListNode pHead2) {
        // write code here
        if (pHead1 == null && pHead2 == null) return null;
        if (pHead1 == null) return pHead2;
        if (pHead2 == null) return pHead1;
        ListNode main = null;
        ListNode cur = null;
        ListNode ptr1 = pHead1;
        ListNode ptr2 = pHead2;
        while (ptr1 != null && ptr2 != null) {
            if (ptr1.val < ptr2.val) {
                if (main == null) {
                    main = ptr1;
                    cur = main;
                } else {
                    cur.next = ptr1;
                    cur = cur.next;
                }
                ptr1 = ptr1.next;
            } else {
                if (main == null) {
                    main = ptr2;
                    cur = main;
                } else {
                    cur.next = ptr2;
                    cur = cur.next;
                }
                ptr2 = ptr2.next;
            }
        }
        if (ptr1 != null) {
            cur.next = ptr1;
        }
        if (ptr2 != null) {
            cur.next = ptr2;
        }
        return main;
    }
}