12. The combined two ordered lists

Subject description:

The two ordered lists into a new sorted list and return. The new list is by all nodes in a given mosaic composed of two lists.
Example:

输入：1->2->4, 1->3->4
输出：1->1->2->3->4->4

Code:

JavaScript

• Recursive method, for a long time did not do recursive problem, a little rusty, recursion is a commonly used method in the list, in this question the idea of ​​a small bit of a backwards move, and then recursively, successively carried out, the outcome .

/**
 * Definition for singly-linked list.
 * function ListNode(val) {
 *     this.val = val;
 *     this.next = null;
 * }
 */
/**
 * @param {ListNode} l1
 * @param {ListNode} l2
 * @return {ListNode}
 */
var mergeTwoLists = function(l1, l2) {
    if (l1 === null) {
        return l2
    }
    if (l2 === null) {
        return l1
    }
    if (l1.val < l2.val) {
        l1.next = mergeTwoLists(l1.next, l2)
        return l1
    } else {
        l2.next = mergeTwoLists(l1, l2.next)
        return l2
    }
};