Merge two sorted linked lists and two sorted lists.

Merge two sorted linked lists and two sorted lists.
Question: enter two linked lists in ascending order, merge these two linked lists, and keep the nodes in the new linked list in ascending order.

Method 1: recursion: Pay attention to the conditions for Recursive termination and the robustness of the Code.

Method 2: Non-recursion. Requires more pointers

1 # include <iostream> 2 # include <stdio. h> 3 # include <tchar. h> 4 5 struct ListNode 6 {7 int m_nValue; 8 ListNode * m_pNext; 9}; 10 11 ListNode * CreateListNode (int value) 12 {13 ListNode * pNode = new ListNode (); 14 pNode-> m_nValue = value; 15 pNode-> m_pNext = NULL; 16 17 return pNode; 18} 19 20 void PrintList (ListNode * pHead) 21 {22 ListNode * pNode = pHead; 23 while (pNode! = NULL) 24 {25 printf ("% d \ t", pNode-> m_nValue); 26 pNode = pNode-> m_pNext; 27} 28 printf ("\ n "); 29} 30 31 void DestroyList (ListNode * pHead) 32 {33 ListNode * pNode = pHead; 34 while (pNode! = NULL) 35 {36 pHead = pHead-> m_pNext; 37 delete pNode; 38 pNode = pHead; 39} 40} 41 42 void ConnectListNodes (ListNode * pCurrent, ListNode * pNext) 43 {44 if (pCurrent = NULL) 45 {46 printf ("Error to connect two nodes. \ n "); 47 exit (1); 48} 49 50 pCurrent-> m_pNext = pNext; 51} 52 53 // method 1 recursion pay attention to code robustness 54 ListNode * Merge1 (ListNode * pHead1, ListNode * pHead2) 55 {56 if (pHead1 = NULL) 57 return PHead2; 58 else if (pHead2 = NULL) 59 return pHead1; 60 61 ListNode * pMergedHead = NULL; 62 63 if (pHead1-> m_nValue <pHead2-> m_nValue) 64 {65 pMergedHead = pHead1; 66 pMergedHead-> m_pNext = Merge1 (pHead1-> m_pNext, pHead2); 67} 68 else 69 {70 pMergedHead = pHead2; 71 pMergedHead-> m_pNext = Merge1 (pHead1, pHead2-> m_pNext); 72} 73 74 return pMergedHead; 75} 76 77 // Method 2: Non-recursion is much more troublesome than recursion, there are also some defined pointers. However, it is easy to understand 78 ListNode * Merge2 (ListNode * pHead1, ListNode * pHead2) 79 {80 if (pHead1 = NULL) 81 return pHead2; 82 if (pHead2 = NULL) 83 return pHead1; 84 85 ListNode * pNode1 = pHead1; 86 ListNode * pNode2 = pHead2; 87 ListNode * pMergedHead = NULL; // The merged linked list header node 88 ListNode * pCurLastNode = NULL; 89 90 if (pNode1-> m_nValue <pNode2-> m_nValue) 91 {92 pMergedHead = pHead1; 93 pNode1 = pNode1-> m_pNext; 94 pC UrLastNode = pMergedHead; 95} 96 else 97 {98 pMergedHead = pHead2; 99 pNode2 = pNode2-> m_pNext; 100 pCurLastNode = pMergedHead; 101} 102 while (pNode1! = NULL & pNode2! = NULL) 104 {105 if (pNode1-> m_nValue <pNode2-> m_nValue) 106 {107 pCurLastNode-> m_pNext = pNode1; 108 pCurLastNode = pNode1; 109 pNode1 = pNode1-> m_pNext; 110} 111 else112 {113 pCurLastNode-> m_pNext = pNode2; 114 pCurLastNode = pNode2; 115 pNode2 = pNode2-> m_pNext; 116} 117 118 if (pNode1 = NULL) 119 pCurLastNode-> m_pNext = pNode2; 120 if (pNode2 = NULL) 121 pCurLastNode-> m_pNext = pNode1; 122} 123 return pMe RgedHead; 124} 125 126 // list1: 1-> 3-> 5127 // list2: 2-> 4-> 6128 129 int main () 130 {131 ListNode * pNode1 = CreateListNode (1); 132 ListNode * pNode3 = CreateListNode (3); 133 ListNode * pNode5 = CreateListNode (5); 134 135 ConnectListNodes (pNode1, pNode3); 136 ConnectListNodes (pNode3, pNode5); 137 138 ListNode * pNode2 = CreateListNode (2); 139 ListNode * pNode4 = CreateListNode (4); 140 ListNode * pNode6 = CreateLis TNode (6); 141 142 ConnectListNodes (pNode2, pNode4); 143 ConnectListNodes (pNode4, pNode6); 144 145 printf ("The first list is: \ n "); 146 PrintList (pNode1); 147 148 printf ("The second list is: \ n"); 149 PrintList (pNode2); 150 151 printf ("The merged list is: \ n "); 152 153 // because the function changes the linked list, it cannot run at the same time. Change true to false to test method 2 154 if (true) 155 {156 printf ("Solution1 \ n"); 157 ListNode * pMergedHead = Merge1 (pNode1, pNode2 ); 158 PrintList (pMergedHead); 159 DestroyList (pMergedHead); 160} 161 else162 {163 printf ("Solution2 \ n"); 164 ListNode * pMergedHead = Merge2 (pNode1, pNode2 ); 165 PrintList (pMergedHead); 166 DestroyList (pMergedHead); 167} 168 169}