leetcode/src/problems/LeetCode232.java at master · codinglin/leetcode · GitHub

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package problems;

import java.util.ArrayDeque;
import java.util.Deque;

public class LeetCode232 {
    Deque<Integer> inStack;
    Deque<Integer> outStack;


    public LeetCode232() {
        inStack = new ArrayDeque<>();
        outStack = new ArrayDeque<>();
    }

    public void push(int x) {
        inStack.push(x);
    }

    public int pop() {
        if(outStack.isEmpty()) {
            while (!inStack.isEmpty()) {
                outStack.push(inStack.pop());
            }
        }
        return outStack.pop();
    }

    public int peek() {
        if(outStack.isEmpty()) {
            while (!inStack.isEmpty()) {
                outStack.push(inStack.pop());
            }
        }
        return outStack.peek();
    }

    public boolean empty() {
        return inStack.isEmpty() && outStack.isEmpty();
    }
}