合并两个有序链表（递归非递归方法）

2024年6月8日 101次阅读

前言： 将两个有序链表合并（链表头结点关键字最小，然后逐个增大）

直接上代码

class Node {
    int val;
    Node next;

    Node(int x) {
        val = x;
    }
}

public class LinkedList {
    public static void main(String[] args) {
        LinkedList l = new LinkedList();
        Node l1 = new Node(1);
        l1.next = new Node(5);
        l1.next.next = new Node(7);

        Node l2 = new Node(3);
        l2.next = new Node(9);
        l2.next.next = new Node(10);

        Node l3 = l.mergeList2(l1, l2);
        Node cur = l3;
        while (cur != null) {
            System.out.print(cur.val+" ");
            cur = cur.next;
        }
    }

    //recursive
    public Node mergeList(Node l1, Node l2) {
        if (l1 == null) {
            return l2;
        }
        if (l2 == null) {
            return l1;
        }
        if (l1.val < l2.val) {
            l1.next = mergeList(l1.next, l2);
            return l1;
        }
        else {
            l2.next = mergeList(l1, l2.next);
            return l2;
        }

    }

    //iteratively
    public Node mergeList2(Node l1, Node l2) {
// if (l1 == null) return l2;//不需要再判断l1,l2是否为空了
// if (l2 == null) return l1;
        Node dummy = new Node(0);//有了假的头,新链表的头结点和非头结点都可以不加区分地追加在链表尾部
        Node cur = dummy;
        while (l1 != null && l2 != null) {
            if (l1.val < l2.val) {
                cur.next = l1;
                l1 = l1.next;
            }
            else {
                cur.next = l2;
                l2 = l2.next;
            }
            cur = cur.next;//当前结点为下一结点
        }
        cur.next = (l1 != null) ? l1 : l2;//归并排序思想

        return dummy.next;//注意返回的是dummy.next
    }

}
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