剑指offer 37 - 两个链表的第一个公共节点

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首先遍历得到两个链表的长度，得到差值dif，较长的链表先移动dif步，然后同时在两个链表上便利，第一个相同的结点就是第一个公共结点
#include<iostream>using namespace std;struct ListNode{int m_nValue;ListNode *m_pNext;};ListNode *CreateListNode(int value){ListNode *node = new  ListNode();node->m_nValue = value;node->m_pNext = NULL;return node;}void ConnectListNodes(ListNode *head,ListNode *next){if(head!=NULL){head->m_pNext = next;}}void DestroyList(ListNode* pHead){ListNode *pNode = pHead;while(pNode!=NULL){pHead = pHead->m_pNext;delete pNode;pNode = pHead;}}void DestroyNode(ListNode* pNode){delete pNode;pNode=NULL;}int getListLength(ListNode * pHead){ListNode *pNode = pHead;int len=0;while(pNode!=NULL){len++;pNode=pNode->m_pNext;}return len;}ListNode * FindFirstCommonNode( ListNode* pHead1, ListNode* pHead2){int pHead1Len = getListLength(pHead1);int pHead2Len = getListLength(pHead2);int difLen = pHead1Len - pHead2Len;ListNode* pLong = pHead1;ListNode* pShort = pHead2;if(difLen<0){difLen = - difLen;pLong = pHead2;pShort = pHead1;}for(int i=0;i<difLen;i++)pLong = pLong->m_pNext;while((pLong!=NULL) && (pShort!=NULL)&& (pLong!=pShort)){pLong = pLong->m_pNext;pShort = pShort->m_pNext;}ListNode *pFirst = pLong;return pFirst;}// ====================测试代码====================void Test(char* testName, ListNode* pHead1, ListNode* pHead2, ListNode* pExpected){    if(testName != NULL)        printf("%s begins: ", testName);    ListNode* pResult = FindFirstCommonNode(pHead1, pHead2);    if(pResult == pExpected)        printf("Passed.\n");    else        printf("Failed.\n");}// 第一个公共结点在链表中间// 1 - 2 - 3 \//            6 - 7//     4 - 5 /void Test1(){    ListNode* pNode1 = CreateListNode(1);    ListNode* pNode2 = CreateListNode(2);    ListNode* pNode3 = CreateListNode(3);    ListNode* pNode4 = CreateListNode(4);    ListNode* pNode5 = CreateListNode(5);    ListNode* pNode6 = CreateListNode(6);    ListNode* pNode7 = CreateListNode(7);    ConnectListNodes(pNode1, pNode2);    ConnectListNodes(pNode2, pNode3);    ConnectListNodes(pNode3, pNode6);    ConnectListNodes(pNode4, pNode5);    ConnectListNodes(pNode5, pNode6);    ConnectListNodes(pNode6, pNode7);    Test("Test1", pNode1, pNode4, pNode6);    DestroyNode(pNode1);    DestroyNode(pNode2);    DestroyNode(pNode3);    DestroyNode(pNode4);    DestroyNode(pNode5);    DestroyNode(pNode6);    DestroyNode(pNode7);}// 没有公共结点// 1 - 2 - 3 - 4//            // 5 - 6 - 7void Test2(){    ListNode* pNode1 = CreateListNode(1);    ListNode* pNode2 = CreateListNode(2);    ListNode* pNode3 = CreateListNode(3);    ListNode* pNode4 = CreateListNode(4);    ListNode* pNode5 = CreateListNode(5);    ListNode* pNode6 = CreateListNode(6);    ListNode* pNode7 = CreateListNode(7);    ConnectListNodes(pNode1, pNode2);    ConnectListNodes(pNode2, pNode3);    ConnectListNodes(pNode3, pNode4);    ConnectListNodes(pNode5, pNode6);    ConnectListNodes(pNode6, pNode7);    Test("Test2", pNode1, pNode5, NULL);    DestroyList(pNode1);    DestroyList(pNode5);}// 公共结点是最后一个结点// 1 - 2 - 3 - 4 \//                7//         5 - 6 /void Test3(){    ListNode* pNode1 = CreateListNode(1);    ListNode* pNode2 = CreateListNode(2);    ListNode* pNode3 = CreateListNode(3);    ListNode* pNode4 = CreateListNode(4);    ListNode* pNode5 = CreateListNode(5);    ListNode* pNode6 = CreateListNode(6);    ListNode* pNode7 = CreateListNode(7);    ConnectListNodes(pNode1, pNode2);    ConnectListNodes(pNode2, pNode3);    ConnectListNodes(pNode3, pNode4);    ConnectListNodes(pNode4, pNode7);    ConnectListNodes(pNode5, pNode6);    ConnectListNodes(pNode6, pNode7);    Test("Test3", pNode1, pNode5, pNode7);    DestroyNode(pNode1);    DestroyNode(pNode2);    DestroyNode(pNode3);    DestroyNode(pNode4);    DestroyNode(pNode5);    DestroyNode(pNode6);    DestroyNode(pNode7);}// 公共结点是第一个结点// 1 - 2 - 3 - 4 - 5// 两个链表完全重合   void Test4(){    ListNode* pNode1 = CreateListNode(1);    ListNode* pNode2 = CreateListNode(2);    ListNode* pNode3 = CreateListNode(3);    ListNode* pNode4 = CreateListNode(4);    ListNode* pNode5 = CreateListNode(5);    ConnectListNodes(pNode1, pNode2);    ConnectListNodes(pNode2, pNode3);    ConnectListNodes(pNode3, pNode4);    ConnectListNodes(pNode4, pNode5);    Test("Test4", pNode1, pNode1, pNode1);    DestroyList(pNode1);}// 输入的两个链表有一个空链表void Test5(){    ListNode* pNode1 = CreateListNode(1);    ListNode* pNode2 = CreateListNode(2);    ListNode* pNode3 = CreateListNode(3);    ListNode* pNode4 = CreateListNode(4);    ListNode* pNode5 = CreateListNode(5);    ConnectListNodes(pNode1, pNode2);    ConnectListNodes(pNode2, pNode3);    ConnectListNodes(pNode3, pNode4);    ConnectListNodes(pNode4, pNode5);    Test("Test5", NULL, pNode1, NULL);    DestroyList(pNode1);}// 输入的两个链表有一个空链表void Test6(){    Test("Test6", NULL, NULL, NULL);}int main(int argc, char* argv[]){    Test1();    Test2();    Test3();    Test4();    Test5();    Test6();    return 0;}
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