leetcode解题之21# Merge Two Sorted Lists Java版 递归和非递归实现

21. Merge Two Sorted Lists

Merge two sorted linked lists and return it as a new list. The new list should be made by splicing together the nodes of the first two lists.

// 非递归实现public ListNode mergeTwoLists(ListNode l1, ListNode l2) {ListNode head = new ListNode(0);ListNode cur = head;while (l1 != null && l2 != null) {if (l1.val >= l2.val) {cur.next = l2;l2 = l2.next;} else {cur.next = l1;l1 = l1.next;}cur = cur.next;}if (l1 != null)cur.next = l1;if (l2 != null)cur.next = l2;return head.next;}// 递归实现public ListNode mergeTwoLists(ListNode l1, ListNode l2) {ListNode res = null;if (l1 == null)return l2;if (l2 == null)return l1;if (l1.val <= l2.val) {res = l1;l1.next = mergeTwoLists(l1.next, l2);} else {res = l2;l2.next = mergeTwoLists(l1, l2.next);}return res;}