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225.implement-stack-using-queues.cpp
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85 lines (77 loc) · 2.15 KB
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// Tag: Stack, Design, Queue
// Time: O(N)
// Space: O(N)
// Ref: -
// Note: -
// Implement a last-in-first-out (LIFO) stack using only two queues. The implemented stack should support all the functions of a normal stack (push, top, pop, and empty).
// Implement the MyStack class:
//
// void push(int x) Pushes element x to the top of the stack.
// int pop() Removes the element on the top of the stack and returns it.
// int top() Returns the element on the top of the stack.
// boolean empty() Returns true if the stack is empty, false otherwise.
//
// Notes:
//
// You must use only standard operations of a queue, which means that only push to back, peek/pop from front, size and is empty operations are valid.
// Depending on your language, the queue may not be supported natively. You may simulate a queue using a list or deque (double-ended queue) as long as you use only a queue's standard operations.
//
//
// Example 1:
//
// Input
// ["MyStack", "push", "push", "top", "pop", "empty"]
// [[], [1], [2], [], [], []]
// Output
// [null, null, null, 2, 2, false]
//
// Explanation
// MyStack myStack = new MyStack();
// myStack.push(1);
// myStack.push(2);
// myStack.top(); // return 2
// myStack.pop(); // return 2
// myStack.empty(); // return False
//
//
// Constraints:
//
// 1 <= x <= 9
// At most 100 calls will be made to push, pop, top, and empty.
// All the calls to pop and top are valid.
//
//
// Follow-up: Can you implement the stack using only one queue?
//
class MyStack {
queue<int> q;
public:
MyStack() {
}
void push(int x) {
q.push(x);
for (int i = 0; i < q.size() - 1; i++) {
q.push(q.front());
q.pop();
}
}
int pop() {
int tmp = top();
q.pop();
return tmp;
}
int top() {
return q.front();
}
bool empty() {
return q.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();
*/