简单实现栈和队列以及其面试题

1.实现基本栈和队列。

（1）栈

#pragma once#include<cassert>#include<string>#include <iostream>using namespace std;template<class T>class Stack{public:Stack():_a(NULL), _size(0), _capacity(0){}~Stack(){if (_a){delete[] _a;_a = NULL;}}void Push(const T& x)//压栈{_Checkcapacity();_a[_size] = x;_size++;}void Pop()//出栈{assert(_size > 0);--_size;}size_t Size(){return _size;}bool Empty()//判断栈是否为空{return _size == 0;}T& Top()//显示栈顶元素{assert(_size > 0);return _a[_size-1];}void _Checkcapacity(){if (_size >= _capacity){size_t newCapacity = _capacity == 0 ? 3 : _capacity * 2;T* tmp = new T[newCapacity];for (size_t i = 0; i < _size; ++i){tmp[i] = _a[i];}delete[] _a;_a = tmp;_capacity = newCapacity;}}protected:T* _a;size_t _size;size_t _capacity;};

//测试代码void TestStack(){Stack<int> s1;s1.Push(1);s1.Push(2);s1.Push(3);s1.Push(4);while (!s1.Empty()){cout << s1.Top() << " ";s1.Pop();}cout << endl;Stack<string> s2;s2.Push("11");s2.Push("22");s2.Push("33");s2.Push("44");while (!s2.Empty()){cout << s2.Top() << " ";s2.Pop();}cout << endl;}

（2）队列

#pragma oncetemplate<class T>struct QueueNode{T _data;QueueNode<T>* _next;QueueNode(const T& x):_data(x), _next(NULL){}};template<class T>class Queue{typedef QueueNode<T> Node;public:Queue():_head(NULL), _tail(NULL){}void Push(const T& x){if (_tail == NULL){_head = _tail = new Node(x);}else{_tail->_next = new Node(x);_tail = _tail->_next;}}void Pop(){if(_head){Node* next = _head->_next;delete _head;_head = next;}}T& Front(){assert(_head);return _head->_data;}size_t Size(){size_t n = 0;Node* cur = _head;while (cur && cur != _tail){++n;cur = cur->_next;}return n;}bool Empty(){return _head == NULL;}protected:Node* _head;Node* _tail;};

//测试代码void TestQueue(){Queue<int> q;q.Push(1);q.Push(2);q.Push(3);q.Push(4);cout << "Size?" << q.Size() << endl;while (!q.Empty()){cout << q.Front() << " ";q.Pop();}cout << endl;}

2.实现栈和队列的面试题。 
（1）实现一个栈，要求实现Push（出栈）、Pop（入栈）、
Min（返回最小值的操作）的时间复杂度为O(1) 

#pragma once#include <stack>#include <iostream>using namespace std;template<class T>class MinStack{public:MinStack(){}void Push(const T& x){s.push(x);if (m.empty() || x < m.top())m.push(x);elsem.push(m.top());}void Pop(){if (!m.empty() || !s.empty()){m.pop();s.pop();}}T& Min(){return m.top();}protected:stack<T> s;stack<T> m;};

（2）使用两个栈实现一个队列

#pragma once#include <stack>#include <iostream>using namespace std;template<class T>class Queue{public:Queue(){}void Push(const T& x){s1.push(x);}void Pop(){if (s1.empty() && s2.empty()){return;}if (s2.empty){while (!s1.empty()){s2.push(s1.top());s1.pop();}}s2.pop();}size_t Size(){return s1.size() + s2.size();}bool Empty(){return (s1.empty() && s2.empty());}T& Front(){if (s1.empty() && s2.empty()){return;}if (s2.empty()){while (!s1.empty()){s2.push(s1.top());s1.pop();}}return s2.top();}protected:stack<T> s1;stack<T> s2;};

（3）使用两个队列实现一个栈 

#pragma once#include <queue>#include <iostream>using namespace std;template<class T>class Stack{public:Stack(){}void Push(const T& x){if (q1.empty() && q2.empty()){q1.push(x);}else if (q1.empty()){q1.push(x);}else{q2.push(x);}}void Pop(){T cur = 0;if (q2.empty()&& (!q1.empty())){while (q1.size() > 1){T& tmp = q1.front();q1.pop();q2.push(tmp);}cur = q1.front();q1.pop();cout << cur << endl;}else if (q1.empty() && (!q2.empty()){while (q2.size() > 1){T& tmp = q2.front();q2.pop();q1.push(tmp);}cur = q2.front();q2.pop();cout << cur << endl;}else{return NULL;}}protected:queue<T> q1;queue<T> q2;};

（4）判断元素出栈、入栈顺序的合法性。如：入栈的序列（1,2,3,4,5），出栈序列为（4,5,3,2,1）是合法序列，入栈的序列（1,2,3,4,5），出栈序列为（1,5,3,2,4）是不合法序列 

#pragma once#include <iostream>#include <stack>using namespace std;bool Judge(int* InArr, int* OutArr, size_t size){stack<int> s;int i = 0;int j = 0;for (size_t i = 0; i < size; i++){s.push(InArr[i]);while (!s.empty() && s.top() == OutArr[j]){s.pop();j++;}}return s.empty();}void TestJudge(){int inarr[5] = { 1, 2, 3, 4, 5 };int outarr[5] = { 4, 5, 2, 3, 1 };cout << Judge(inarr, outarr, 5) << endl;}

（5）一个数组实现两个栈

template<class T>class TwoStack{public:TwoStack():_a(NULL), _sz1(0), _sz2(0), _capacity(0){_CheckCapacity();}~TwoStack(){if (_a)delete[] _a;}void Push1(const T& d){_CheckCapacity();_a[_sz1++] = d;}void Push2(const T& d){_CheckCapacity();_a[_sz2--] = d;}void Pop1(){if (_sz1 > 0)--_sz1;}void Pop2(){if (_sz2 < _capacity - 1)_sz2++;}size_t Size1(){return _sz1;}size_t Size2(){return _capacity - 1 - _sz2;}bool Empty1(){return _sz1 == 0;}bool Empty2(){return _sz2 == _capacity - 1;}T& Top1(){if (_sz1>0){return _a[_sz1 - 1];}}T& Top2(){if (_sz2 < _capacity - 1)return _a[_sz2 + 1];}private:void _CheckCapacity(){if (_a == NULL){_capacity += 3;_a = new T[_capacity];_sz2 = _capacity - 1;return;}if (_sz1 == _sz2){size_t OldCapacity = _capacity;_capacity = _capacity * 2;T* tmp = new T[_capacity];for (size_t i = 0; i < _sz1; i++){tmp[i] = _a[i];}for (size_t j = OldCapacity - 1, i = _capacity - 1; j>_sz2; j--, i--){tmp[i] = _a[j];}delete[] _a;_a = tmp;_sz2 += _capacity / 2;}}private:T* _a;size_t _sz1;size_t _sz2;size_t _capacity;};

//测试代码

void TestTwoStack(){TwoStack<int> s;s.Push1(1);s.Push1(2);s.Push1(3);s.Push1(4);s.Push1(5);s.Push2(1);s.Push2(2);s.Push2(3);s.Push2(4);s.Push2(5);cout << "s1:" << s.Size1() << endl;cout << "s2:" << s.Size2() << endl;while (!s.Empty1()){cout << s.Top1() << endl;s.Pop1();}while (!s.Empty2()){cout << s.Top2() << endl;s.Pop2();}}