public class MyStack {
/** Initialize your data structure here. */
Queue<Integer> pq = new LinkedList<Integer>();
public MyStack() {
}
/** Push element x onto stack. */
public void push(int x) {
pq.add(x);
for(int i=1;i<pq.size();i++)
pq.add(pq.poll());
}
/** Removes the element on top of the stack and returns that element. */
public int pop() {
return pq.poll();
}
/** Get the top element. */
public int top() {
return pq.peek();
}
/** Returns whether the stack is empty. */
public boolean empty() {
return pq.isEmpty();
}
}
/**
* 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();
* boolean param_4 = obj.empty();
*/
用隊列實現(xiàn)堆棧，關(guān)鍵在于push的時候，將隊列中的所有數(shù)反轉(zhuǎn)一遍遣疯。
232. Implement Queue using Stacks
public class MyQueue {
/** Initialize your data structure here. */
Stack<Integer> in = new Stack();
Stack<Integer> out = new Stack();
public MyQueue() {
}
/** Push element x to the back of queue. */
public void push(int x) {
in.push(x);
}
/** Removes the element from in front of queue and returns that element. */
public int pop() {
peek();
return out.pop();
}
/** Get the front element. */
public int peek() {
if(out.isEmpty()){
while(!in.isEmpty())
out.push(in.pop());
}
return out.peek();
}
/** Returns whether the queue is empty. */
public boolean empty() {
return in.isEmpty()&&out.isEmpty();
}
}
/**
* 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();
* boolean param_4 = obj.empty();
*/
用堆棧實現(xiàn)隊列清酥，技術(shù)點在維護兩個堆棧扶镀。
