合并两个有序链表（递归非递归方法）

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
}

}