文章作者：Tyan
博客：noahsnail.com | CSDN |
1. Description
Implement Stack using Queues
2. Solution
- Version 1
class MyStack {
public:
/** Initialize your data structure here. */
MyStack() {
}
/** Push element x onto stack. */
void push(int x) {
q1.push(x);
top_value = x;
}
/** Removes the element on top of the stack and returns that element. */
int pop() {
while(q1.size() != 1) {
q2.push(q1.front());
q1.pop();
}
int value = q1.front();
q1.pop();
q1 = q2;
while(!q2.empty()) {
top_value = q2.front();
q2.pop();
}
return value;
}
/** Get the top element. */
int top() {
return top_value;
}
/** Returns whether the stack is empty. */
bool empty() {
return q1.empty() && q2.empty();
}
private:
queue q1;
queue q2;
int top_value;
};
/**
* Your MyStack object will be instantiated and called as such:
* MyStack obj = new MyStack();
* obj.push(x);
* int param_2 = obj.pop();
* int param_3 = obj.top();
* bool param_4 = obj.empty();
*/
- Version 2
class MyStack {
public:
/** Initialize your data structure here. */
MyStack() {
}
/** Push element x onto stack. */
void push(int x) {
q.push(x);
top_value = x;
}
/** Removes the element on top of the stack and returns that element. */
int pop() {
queue temp;
while(q.size() != 1) {
temp.push(q.front());
top_value = q.front();
q.pop();
}
int value = q.front();
q.pop();
q = temp;
return value;
}
/** Get the top element. */
int top() {
return top_value;
}
/** Returns whether the stack is empty. */
bool empty() {
return q.empty();
}
private:
queue q;
int top_value;
};
/**
* Your MyStack object will be instantiated and called as such:
* MyStack obj = new MyStack();
* obj.push(x);
* int param_2 = obj.pop();
* int param_3 = obj.top();
* bool param_4 = obj.empty();
*/
Reference
- https://leetcode.com/problems/implement-stack-using-queues/description/