JZ-C-37

剑指offer第三十七题：两个链表的第一个公共结点

  1 //============================================================================
  2 // Name        : JZ-C-37.cpp
  3 // Author      : Laughing_Lz
  4 // Version     :
  5 // Copyright   : All Right Reserved
  6 // Description : 两个链表的第一个公共结点
  7 //============================================================================
  8
  9 #include <iostream>
 10 #include <stdio.h>
 11 #include "List.h"
 12 using namespace std;
 13
 14 unsigned int GetListLength(ListNode* pHead);
 15 /**
 16  * 先移动长链表指针至某位置（与短链表持平），再同时遍历，遇到第一个相同的结点即为公共结点
 17  * 时间复杂度为O(m+n)
 18  */
 19 ListNode* FindFirstCommonNode(ListNode *pHead1, ListNode *pHead2) {
 20     // 得到两个链表的长度
 21     unsigned int nLength1 = GetListLength(pHead1);
 22     unsigned int nLength2 = GetListLength(pHead2);
 23     int nLengthDif = nLength1 - nLength2;
 24
 25     ListNode* pListHeadLong = pHead1;
 26     ListNode* pListHeadShort = pHead2;
 27     if (nLength2 > nLength1) {
 28         pListHeadLong = pHead2;
 29         pListHeadShort = pHead1;
 30         nLengthDif = nLength2 - nLength1;
 31     }
 32
 33     // 先在长链表上走几步，再同时在两个链表上遍历
 34     for (int i = 0; i < nLengthDif; ++i)
 35         pListHeadLong = pListHeadLong->m_pNext;
 36
 37     while ((pListHeadLong != NULL) && (pListHeadShort != NULL)
 38             && (pListHeadLong != pListHeadShort)) {
 39         pListHeadLong = pListHeadLong->m_pNext;//当不存在公共结点时，返回NULL
 40         pListHeadShort = pListHeadShort->m_pNext;
 41     }
 42
 43     // 得到第一个公共结点
 44     ListNode* pFisrtCommonNode = pListHeadLong;
 45
 46     return pFisrtCommonNode;
 47 }
 48
 49 unsigned int GetListLength(ListNode* pHead) {
 50     unsigned int nLength = 0;
 51     ListNode* pNode = pHead;
 52     while (pNode != NULL) {
 53         ++nLength;
 54         pNode = pNode->m_pNext;
 55     }
 56
 57     return nLength;
 58 }
 59
 60 // ====================测试代码====================
 61 void DestroyNode(ListNode* pNode);
 62
 63 void Test(char* testName, ListNode* pHead1, ListNode* pHead2,
 64         ListNode* pExpected) {
 65     if (testName != NULL)
 66         printf("%s begins: ", testName);
 67
 68     ListNode* pResult = FindFirstCommonNode(pHead1, pHead2);
 69     if (pResult == pExpected)
 70         printf("Passed.\n");
 71     else
 72         printf("Failed.\n");
 73 }
 74
 75 // 第一个公共结点在链表中间
 76 // 1 - 2 - 3  77 //            6 - 7
 78 //     4 - 5 /
 79 void Test1() {
 80     ListNode* pNode1 = CreateListNode(1);
 81     ListNode* pNode2 = CreateListNode(2);
 82     ListNode* pNode3 = CreateListNode(3);
 83     ListNode* pNode4 = CreateListNode(4);
 84     ListNode* pNode5 = CreateListNode(5);
 85     ListNode* pNode6 = CreateListNode(6);
 86     ListNode* pNode7 = CreateListNode(7);
 87
 88     ConnectListNodes(pNode1, pNode2);
 89     ConnectListNodes(pNode2, pNode3);
 90     ConnectListNodes(pNode3, pNode6);
 91     ConnectListNodes(pNode4, pNode5);
 92     ConnectListNodes(pNode5, pNode6);
 93     ConnectListNodes(pNode6, pNode7);
 94
 95     Test("Test1", pNode1, pNode4, pNode6);
 96
 97     DestroyNode(pNode1);
 98     DestroyNode(pNode2);
 99     DestroyNode(pNode3);
100     DestroyNode(pNode4);
101     DestroyNode(pNode5);
102     DestroyNode(pNode6);
103     DestroyNode(pNode7);
104 }
105
106 // 没有公共结点
107 // 1 - 2 - 3 - 4
108 //
109 // 5 - 6 - 7
110 void Test2() {
111     ListNode* pNode1 = CreateListNode(1);
112     ListNode* pNode2 = CreateListNode(2);
113     ListNode* pNode3 = CreateListNode(3);
114     ListNode* pNode4 = CreateListNode(4);
115     ListNode* pNode5 = CreateListNode(5);
116     ListNode* pNode6 = CreateListNode(6);
117     ListNode* pNode7 = CreateListNode(7);
118
119     ConnectListNodes(pNode1, pNode2);
120     ConnectListNodes(pNode2, pNode3);
121     ConnectListNodes(pNode3, pNode4);
122     ConnectListNodes(pNode5, pNode6);
123     ConnectListNodes(pNode6, pNode7);
124
125     Test("Test2", pNode1, pNode5, NULL);
126
127     DestroyList(pNode1);
128     DestroyList(pNode5);
129 }
130
131 // 公共结点是最后一个结点
132 // 1 - 2 - 3 - 4 133 //                7
134 //         5 - 6 /
135 void Test3() {
136     ListNode* pNode1 = CreateListNode(1);
137     ListNode* pNode2 = CreateListNode(2);
138     ListNode* pNode3 = CreateListNode(3);
139     ListNode* pNode4 = CreateListNode(4);
140     ListNode* pNode5 = CreateListNode(5);
141     ListNode* pNode6 = CreateListNode(6);
142     ListNode* pNode7 = CreateListNode(7);
143
144     ConnectListNodes(pNode1, pNode2);
145     ConnectListNodes(pNode2, pNode3);
146     ConnectListNodes(pNode3, pNode4);
147     ConnectListNodes(pNode4, pNode7);
148     ConnectListNodes(pNode5, pNode6);
149     ConnectListNodes(pNode6, pNode7);
150
151     Test("Test3", pNode1, pNode5, pNode7);
152
153     DestroyNode(pNode1);
154     DestroyNode(pNode2);
155     DestroyNode(pNode3);
156     DestroyNode(pNode4);
157     DestroyNode(pNode5);
158     DestroyNode(pNode6);
159     DestroyNode(pNode7);
160 }
161
162 // 公共结点是第一个结点
163 // 1 - 2 - 3 - 4 - 5
164 // 两个链表完全重合
165 void Test4() {
166     ListNode* pNode1 = CreateListNode(1);
167     ListNode* pNode2 = CreateListNode(2);
168     ListNode* pNode3 = CreateListNode(3);
169     ListNode* pNode4 = CreateListNode(4);
170     ListNode* pNode5 = CreateListNode(5);
171
172     ConnectListNodes(pNode1, pNode2);
173     ConnectListNodes(pNode2, pNode3);
174     ConnectListNodes(pNode3, pNode4);
175     ConnectListNodes(pNode4, pNode5);
176
177     Test("Test4", pNode1, pNode1, pNode1);
178
179     DestroyList(pNode1);
180 }
181
182 // 输入的两个链表有一个空链表
183 void Test5() {
184     ListNode* pNode1 = CreateListNode(1);
185     ListNode* pNode2 = CreateListNode(2);
186     ListNode* pNode3 = CreateListNode(3);
187     ListNode* pNode4 = CreateListNode(4);
188     ListNode* pNode5 = CreateListNode(5);
189
190     ConnectListNodes(pNode1, pNode2);
191     ConnectListNodes(pNode2, pNode3);
192     ConnectListNodes(pNode3, pNode4);
193     ConnectListNodes(pNode4, pNode5);
194
195     Test("Test5", NULL, pNode1, NULL);
196
197     DestroyList(pNode1);
198 }
199
200 // 输入的两个链表有一个空链表
201 void Test6() {
202     Test("Test6", NULL, NULL, NULL);
203 }
204
205 void DestroyNode(ListNode* pNode) {
206     delete pNode;
207     pNode = NULL;
208 }
209
210 int main(int argc, char** argv) {
211     Test1();
212     Test2();
213     Test3();
214     Test4();
215     Test5();
216     Test6();
217
218     return 0;
219 }