Merge Two Sorted Lists.cpp

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode *mergeTwoLists(ListNode *l1, ListNode *l2) {
        if (!l1)    return l2;
        if (!l2)    return l1;
        ListNode *ret, *cur;
        if (l1->val < l2->val) {
            ret = l1;
            l1 = l1->next;
        } else {
            ret = l2;
            l2 = l2->next;
        }
        cur = ret;
        while (l1 && l2) {
            if (l1->val < l2->val) { 
                cur->next = l1;
                l1 = l1->next;
            }
            else {
                cur->next = l2;
                l2 = l2->next;
            }
            cur = cur->next;
        }
        if (l1) cur->next = l1;
        if (l2) cur->next = l2;
        return ret;
    }
};