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Copy pathstack2queue.cpp
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171 lines (158 loc) · 3.33 KB
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#include <iostream>
#include <stack>
#include <algorithm>
using namespace std;
/*
* 用两个栈：push栈和pop栈
* push栈往pop栈中倒数据时遵循两个原则：
* 1 pop栈必须是空的才可以倒
* 2 push栈每次倒数据必须把push栈中的数据全部倒到pop栈中不能有剩余
* 遵循以上两个原则后，则倒数据的动作可以发生在任何时候。
*/
class MyQueue{
private:
stack<int> stackpush, stackpop;
public:
MyQueue(){
}
void push(int obj){
stackpush.push(obj);
//swap_push_and_pop();
}
void pop(){
swap_push_and_pop();
stackpop.pop();
}
// 返回队列头部元素
int front(){
if (stackpush.empty() && stackpop.empty()){
cerr << "your queue is empty" << endl;
return NULL;
}
// 队列头部元素即push栈栈底元素,即pop栈栈顶元素
swap_push_and_pop();
return stackpop.top();
}
// 返回队列底部元素
int back(){
// 队列底部元素即push栈栈顶元素
if (stackpush.empty() && stackpop.empty()){
cerr << "your queue is empty" << endl;
return NULL;
}
//swap_push_and_pop();
return stackpush.top();
}
int size(){
return stackpush.size();
}
void swap_push_and_pop(){
if (stackpop.empty()){
while (!stackpush.empty()){
int tmp = stackpush.top();
stackpop.push(tmp);
stackpush.pop();
}
}
}
};
// 另一个想法：用两个栈：数据栈和辅助栈，pop和front的时候将数据栈的数据除了栈底外均导入辅助栈
// 删掉栈底(因为数据栈只剩这一个元素，也即栈顶),然后再将辅助栈的元素逐个弹出并压回数据栈
class MyQueue2{
private:
stack<int> data,help;
public:
MyQueue2(){
}
void push(int obj){
data.push(obj);
}
void pop(){
if (data.empty()){
cerr << "your queue is empty";
}
else if (data.size() == 1){
data.pop();
}
else{
int datasize = data.size();
for (int i = 0; i < datasize - 1; i++){
int tmp = data.top();
data.pop();
help.push(tmp);
}
data.pop();
int helpsize = help.size();
for (int i = 0; i < helpsize; i++){
int tmp = help.top();
help.pop();
data.push(tmp);
}
}
}
int front(){
if (data.empty()){
cerr << "your queue is empty";
return NULL;
}
else if (data.size() == 1){
return data.top();
}
else{
int datasize = data.size();
for (int i = 0; i < datasize - 1; i++){
int tmp = data.top();
data.pop();
help.push(tmp);
}
int result = data.top();
//data.pop();
int helpsize = help.size();
for (int i = 0; i < helpsize; i++){
int tmp = help.top();
help.pop();
data.push(tmp);
}
data.push(result);
return result;
}
}
int back(){
return data.top();
}
int size(){
return data.size();
}
};
int main(){
MyQueue q1;
cout << "befroe pop: ";
for (int i = 0; i < 20; i++){
q1.push(i);
cout << q1.back() << " ";
}
cout << endl;
cout << "q1.front: "<<q1.front() << endl;
cout << "after pop,q1.front: ";
for (int i = 0; i < 20; i++){
cout << q1.front() << " ";
q1.pop();
}
cout << endl;
MyQueue2 q2;
cout << "befroe pop: ";
for (int i = 0; i < 20; i++){
q2.push(i);
cout << q2.back() << " ";
}
cout << endl;
cout << "q2.front: " << q2.front() << endl;
cout << "after pop,q1.front: ";
for (int i = 0; i < 20; i++){
cout << q2.front() << " ";
q2.pop();
}
cout << endl;
system("pause");
return 0;
}