合并两个排序的链表

输入两个单调递增的链表，输出两个链表合成后的链表，当然我们需要合成后的链表满足单调不减规则。

/*
struct ListNode {
	int val;
	struct ListNode *next;
	ListNode(int x) :
			val(x), next(NULL) {
	}
};*/
class Solution {
public:
    ListNode* Merge(ListNode* pHead1, ListNode* pHead2)
    {
        ListNode * const head = new ListNode(INT_MIN);
        ListNode *current = head;
        ListNode *a = pHead1, *b = pHead2;
        while (true)
        {
            if (a == nullptr)
            {
                if (b == nullptr)
                {
                    break;
                }
                else
                {
                    current->next = b;
                    break;
                }
            }
            else
            {
                if (b == nullptr)
                {
                    current->next = a;
                    break;
                }
                else
                {
                    if (a->val < b->val)
                    {
                        current->next = new ListNode(a->val);
                        current = current->next;
                        a = a->next;
                    }
                    else
                    {
                        current->next = new ListNode(b->val);
                        current = current->next;
                        b = b->next;
                    }
                }
            }
        }
        ListNode * const first = head->next;
        delete head;
        return first;
    }
};