Implement the following operations of a queue using stacks.
push(x) -- Push element x to the back of the queue. pop() -- Removes the element from in front of the queue. peek() -- Get the front element. empty() -- Return whether the queue is empty. Notes:
You must use only standard operations of a stack -- which means only push to top, peek/pop from top, size, and is empty operations are valid. Depending on your language, the stack may not be supported natively. You may simulate a stack by using a list or deque (double-ended queue), as long as you use only standard operations of a stack. You may assume that all operations are valid (for example, no pop or peek operations will be called on an empty queue).
Example 1:
Input ["MyQueue", "push", "push", "peek", "pop", "empty"] [[], [1], [2], [], [], []] Output [null, null, null, 1, 1, false]
Explanation MyQueue myQueue = new MyQueue(); myQueue.push(1); myQueue.push(2); myQueue.peek(); // return 1 myQueue.pop(); // return 1 myQueue.empty(); // return False
Constraints:
1 <= x < 10 At most 100 calls will be made to push, pop, peek, and empty.
public class MyQueue {
Stack<int> stack1;
Stack<int> stack2;
/** Initialize your data structure here. */
public MyQueue() {
stack1 = new Stack<int>();
stack2 = new Stack<int>();
}
/** Push element x to the back of queue. */
public void Push(int x) {
stack1.Push(x);
}
/** Removes the element from in front of queue and returns that element. */
public int Pop() {
if(stack2.Count()<1){
while(stack1.Count()>0){
stack2.Push(stack1.Pop());
}
}
return stack2.Pop();
}
/** Get the front element. */
public int Peek() {
if(stack2.Count<1){
while(stack1.Count()>0){
stack2.Push(stack1.Pop());
}
}
return stack2.Peek();
}
/** Returns whether the queue is empty. */
public bool Empty() {
return stack1.Count()<1 && stack2.Count()<1;
}
}
/**
* Your MyQueue object will be instantiated and called as such:
* MyQueue obj = new MyQueue();
* obj.Push(x);
* int param_2 = obj.Pop();
* int param_3 = obj.Peek();
* bool param_4 = obj.Empty();
*/Time Complexity: O(n)
Space Complexity: O(n)
