Problem
Implement the following operations of a stack using queues.
- push(x) -- Push element x onto stack.
- pop() -- Removes the element on top of the stack.
- top() -- Get the top element.
- empty() -- Return whether the stack is empty.
Notes:
- You must use only standard operations of a queue -- which means only push to back, peek/pop from front, size, and is empty operations are valid.
- Depending on your language, queue may not be supported natively. You may simulate a queue by using a list or deque (double-ended queue), as long as you use only standard operations of a queue.
- You may assume that all operations are valid (for example, no pop or top operations will be called on an empty stack).
Example
MyStack stack = new MyStack();
stack.push(1);
stack.push(2);
stack.top(); // returns 2
stack.pop(); // returns 2
stack.empty(); // returns false
Code
static int var = [](){
std::ios::sync_with_stdio(false);
cin.tie(NULL);
return 0;
}();
class MyStack {
private:
queue<int> stack;
public:
/** Initialize your data structure here. */
MyStack() {
}
/** Push element x onto stack. */
void push(int x) {
stack.push(x);
}
/** Removes the element on top of the stack and returns that element. */
int pop() {
int temp = 0;
for(int i=0;i<stack.size()-1;i++){
temp = stack.front();
stack.pop();
stack.push(temp);
}
temp = stack.front();
stack.pop();
return temp;
}
/** Get the top element. */
int top() {
int temp = 0;
for(int i=0;i<stack.size()-1;i++){
temp = stack.front();
stack.pop();
stack.push(temp);
}
temp = stack.front();
stack.pop();
stack.push(temp);
return temp;
}
/** Returns whether the stack is empty. */
bool empty() {
return stack.empty();
}
};
/**
* 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();
*/
Result
225. Implement Stack using Queues.png
