Implement Queue using Stacks

这种基础题，为啥自己一开始的设计总是能想出很邪门的思路来，又是两个stack一起用，于是要用bool来控制用哪个stack，进而lock，线程保护等等就全出来了。。。

想上天啊！！

class MyQueue {

//boolean pushS1 = true;
Stack<Integer> s1 = new Stack<>();
Stack<Integer> s2 = new Stack<>();

// Push element x to the back of queue.
public void push(int x) {
s1.push(x);
// if (pushS1) {
// s1.push(x);
// } else {
// s2.push(x);
// }
}

// Removes the element from in front of queue.
public void pop() {
// if (pushS1) {
// pushS1 = false;
// }
if (!s2.isEmpty()) {
s2.pop();
} else {
while (!s1.isEmpty()) {
s2.push(s1.pop());
}
////
s2.pop();
////
}
}

// Get the front element.
public int peek() {
if (!s2.isEmpty()) {
return s2.peek();
} else {
while (!s1.isEmpty()) {
s2.push(s1.pop());
}
return s2.peek();
}
}

// Return whether the queue is empty.
public boolean empty() {
return s1.isEmpty() && s2.isEmpty();
}
}