struct ListNode {  int val;  struct ListNode *next;  ListNode(int x) :  val(x), next(NULL) {  }};

class Solution {public:  ListNode* Merge(ListNode* pHead1, ListNode* pHead2)  {    ListNode* newList = NULL; //新鏈表頭    ListNode* newListRear = NULL; //新鏈表尾    // 先處理某個鏈表為空的情形    if (pHead1 == NULL){      return pHead2;    }    if (pHead2 == NULL){      return pHead1;    }    // 把數值小的結點放入新鏈表，生成頭節點    if (pHead1->val <= pHead2->val){      newList = pHead1;      newListRear = pHead1;      pHead1 = pHead1->next;    }else{      newList = pHead2 ;      newListRear = pHead2;      pHead2 = pHead2->next;    }    // 兩表均不空的情形下，遍歷     while (pHead1 != NULL && pHead2 != NULL) {      if (pHead1->val <= pHead2->val) {        newListRear->next =pHead1;        newListRear = pHead1;        pHead1 = pHead1->next;      }else{        newListRear->next =pHead2;        newListRear = pHead2;        pHead2 = pHead2->next;      }    }    //某一表為空時，把另一表接入新表表尾     if (pHead1 == NULL) {      newListRear->next = pHead2;    }    if (pHead2 == NULL) {      newListRear->next = pHead1;    }        return newList;  }};

class Solution {public:  ListNode* Merge(ListNode* pHead1, ListNode* pHead2)  {    if (pHead1 == NULL){      return pHead2;    }    if (pHead2 == NULL){      return pHead1;    }        if (pHead1->val <= pHead2->val){ // pHead1為合并后的頭節點      pHead1->next = Merge(pHead1->next, pHead2);      return pHead1;    }else{ // pHead2 為合并后的頭節點      pHead2->next = Merge(pHead1, pHead2->next);      return pHead2;    }  }};