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import java.util.Stack;

/**

* https://leetcode.com/articles/implement-queue-using-stacks/

*/

public class MyQueue {

private Stack<Integer> mStack = new Stack<Integer>();

private Stack<Integer> mStackTmp = new Stack<Integer>();

// Push element x to the back of queue.

public void push(int x) {

mStack.push(x);

}

// Removes the element from in front of queue.

public void pop() {

dump(mStack, mStackTmp);

mStackTmp.pop();

dump(mStackTmp, mStack);

}

// Get the front element.

public int peek() {

dump(mStack, mStackTmp);

int peek = mStackTmp.peek();

dump(mStackTmp, mStack);

return peek;

}

// Return whether the queue is empty.

public boolean empty() {

return mStack.isEmpty();

}

private void dump(Stack<Integer> left, Stack<Integer> right) {

while (!left.isEmpty()) {

right.push(left.pop());

}

}

}