两个栈实现队列
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#include <iostream> #include <stack> using namespace std; template <class T> class MyQueue { public: bool empty()const { return head.empty()&&tail.empty(); } void push(T t) { head.push(t); } //删除对头元素 //因为queue是一种先进先出，而stack是先进后出，所以需要把head里的数据拷贝到tail中然后再从tail中pop头元素 void pop() { if(this->empty()) { //throw exception("队列为NULL"); } while(!head.empty()) { tail.push(head.top()); head.pop(); } //删除头元素 tail.pop(); //再将队尾栈容器元素拷贝到队头栈容器中 while(!tail.empty()) { head.push(tail.top()); tail.pop(); } } T& back() { if(this->empty()) { // throw exception("head is NULL"); } return head.top(); } //返回第一个元素 T& front() { if(this->empty()) { //throw exception("队列为NULL"); } while(!head.empty()) { tail.push(head.top()); head.pop(); } int tmp = tail.top(); //再将队尾栈容器元素拷贝到队头栈容器中 while(!tail.empty()) { head.push(tail.top()); tail.pop(); } return tmp; } private: stack<int> head; stack<int> tail; }; int main() { MyQueue<int> q; for(int i=1;i<5;i++) { q.push(i); } cout<<"front:"<<q.front()<<endl; cout<<"back:"<<q.back()<<endl; return 0; } |
链表反转
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#include<iostream> #include<cstdlib> using namespace std; class list{ public: int data; class list *next; }; typedef class list node; typedef node *link; link FindNode(link head,int position_data){ link phead; phead = head; while(phead != NULL){ if(phead->data == position_data)return phead; phead = phead->next; } return phead; } link InsertNode(link head,int position_data,int data){ link phead = new node; phead = FindNode(head,position_data); link insertnode = new node; if(!insertnode) return NULL; insertnode->data = data; insertnode->next = NULL; if(phead == NULL){ //插入第一个节点 insertnode->next = head; return insertnode; } else if(phead->next == NULL) phead->next = insertnode; //插入最后一个节点 else{ //插入中间节点 insertnode->next = phead->next; phead->next = insertnode; } return head; } link DeleteNode(link head,int position_data){ link top = head; //保留头指针 link phead = FindNode(head,position_data); if(head == phead){ //删除头结点 head = head->next; delete phead; } else{ while(top->next != phead) top = top->next; if(phead->next == NULL){ //删除尾结点 top->next = NULL; delete phead; } else{ top->next = phead->next; delete phead; } } return head; } link InvertList(link head){ link pre,phead,temp; phead = head; //将phead指向链表头，做游标使用 pre = NULL; //pre为头指针之前的节点 while(phead != NULL){ temp = pre; pre = phead; phead = phead->next; pre->next = temp; //pre接到之前的节点 } return pre; } link CreateList(int a[],int n){ link head,phead,newnode; phead = new node; if(!phead) return NULL; phead->data = a[0]; head = phead; for(int i = 1;i<n;i++){ newnode = new node; newnode->data = a[i]; newnode->next = NULL; phead->next = newnode; phead = phead->next; } return head; } void PrintList(link head){ link phead = new node; phead = head; cout<<"链表元素如下: "<<endl; while(phead!=NULL){ cout<<phead->data<<"->"; head = phead; phead = phead->next; //phead按序往后遍历整个链表 if(!phead) cout<<"NULL"<<endl; } } int main(){ int position_data,data; link head,phead; int n; cout<<"请输入初始链表元素个数: "<<endl; cin>>n; int a[n]; cout<<"请依次输入链表元素: "; for(int i = 0;i<n;i++) cin>>a[i]; head = CreateList(a,n); PrintList(head); cout<<"请输入预插入位置之前的元素和要插入的元素（例：5 8）: "; cin>>position_data>>data; head = InsertNode(head,position_data,data); cout<<"插入之后的"; PrintList(head); cout<<"请输入想删除的链表元素: "; cin>>position_data; head = DeleteNode(head,position_data); cout<<"删除之后的"; PrintList(head); cout<<"反转之后的"; head = InvertList(head); PrintList(head); return 0; } |
快速排序
TCP三次握手
野指针
指针指向的位置是不可知的(随机的、不正确的、没有明确限制的)
野指针很可能触发运行时段错误(Sgmentation fault)
- 第一种是指向不可访问(操作系统不允许访问的敏感地址，譬如内核空间)的地址，结果是触发段错误，这种算是最好的情况了
- 第二种是指向一个可用的、而且没什么特别意义的空间，这时候程序运行不会出错，也不会对当前程序造成损害，这种情况下会掩盖你的程序错误，让你以为程序没问题，其实是有问题的
- 第三种情况就是指向了一个可用的空间，而且这个空间其实在程序中正在被使用
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