LeetCode Reverse Linked List II
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用插入法实现链表的倒序,对于是否从第一个元素开始的情况分别对待,没测试提交,第一次居然犯了太低级的错误了;这题给出了一个前提保证了m小于等于n小于等于链表长度,所以程序里不用担心链表在任何时候走过了(那样的话处处都得判断指针是否为空),我想说的是在没给出这样条件的时候,自己编程时也应该这样考虑,编写的函数假设输入合法,对于不合法的输入应该预先做一下判断,并且封装在另一个函数里,这样把核心算法与输入条件判断确实简化了编程,之前也在某些书上看过,这次是真有体会。
// LeetCode_ReverseLinkedListII.cpp : 定义控制台应用程序的入口点。//#include "stdafx.h"#include <iostream>using namespace std; struct ListNode { int val; ListNode *next; ListNode(int x) : val(x), next(NULL) {}};ListNode *reverseBetween(ListNode *head, int m, int n) {if(m==n||head==NULL||head->next==NULL)return head;ListNode *s=head,*p=s->next,*q=NULL;int k=n-m;;if(m==1){while(k>0){s->next = p->next;p->next = head;head = p;p = s->next;k--;}}else{q = p->next;while(m>2){s = p;p = q;q = q->next;m--;}while(k>0){p->next = q->next;q->next = s->next;s->next = q;q = p->next;k--;}}return head;}int _tmain(int argc, _TCHAR* argv[]){/*ListNode *a = new ListNode(6); ListNode *b = new ListNode(5); ListNode *c = new ListNode(3); ListNode *d = new ListNode(1); */ ListNode *e = new ListNode(1); ListNode *f = new ListNode(4); /*a->next = b; b->next = c; c->next = d; d->next = e; */e->next = f; ListNode *rethead=NULL; rethead = reverseBetween(e,1,2); ListNode *p = rethead; while(p!=NULL) { cout<<p->val<<" "; p = p->next; } system("pause"); return 0;}
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