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  1. Queue using Two Stacks
  2. Discussions

Queue using Two Stacks

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26 Discussions

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  • jimiwills
     + 0 comments

    i don't really understand why it's asking to do it with 2 stacks

    class Solution {
    private static List<int> oneStack = new List<int>();

    static void Main(String[] args) {
        var q = int.Parse(Console.In.ReadLine()!.TrimEnd()); // number of queries
        for(var i=0; i<q; i++){
            var a = Console.In.ReadLine()!.TrimEnd().Split(" ").Select(x => int.Parse(x)).ToArray();
            var t = a[0];
            switch(t){
                case 1:
                    enqueue(a[1]);
                    break;
                case 2:
                    dequeue();
                    break;
                case 3: 
                    print();
                    break;
                default:
                    throw new Exception($"t={t}");
            }
        }
    }

    static void enqueue(int x){
        oneStack.Add(x);
    }

    static void dequeue(){
        oneStack = oneStack.Skip(1).ToList();
    }

    static void print(){
        Console.WriteLine(oneStack.First());
    }
}

  • inq_daniel_eliz1
     + 0 comments

    My answer in Python

    q = int(input())
inpts = []

for i in range(q):
    inpts.append(input())


ans = []

for i in inpts:
    if i[0] == "1":
        j, num = i.split(" ")
        ans.append(int(num))
    elif i[0] == "2":
        ans.pop(0)
    elif i[0] == "3":
        print(ans[0])

  • vadym_usatiuk
     + 0 comments

    Java and O(1)

    public static class QueueUsingTwoStacks<T> {
        private Stack<T> stack1; 
        private Stack<T> stack2; 
        
        public QueueUsingTwoStacks() {
            stack1 = new Stack<>();
            stack2 = new Stack<>();
        }
        
        public void enqueue(T element) {
            stack1.push(element);
        }
        
        public T dequeue() {
            if (stack2.isEmpty()) {
                while (!stack1.isEmpty()) {
                    stack2.push(stack1.pop());
                }
            }
            return stack2.pop();
        }
        
        public T peek() {
            if (stack2.isEmpty()) {
                while (!stack1.isEmpty()) {
                    stack2.push(stack1.pop());
                }
            }
            return stack2.peek();
        }
    }

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int q = scanner.nextInt();
        QueueUsingTwoStacks<Integer> queue = new QueueUsingTwoStacks<>();
        
        for (int i = 0; i < q; i++) {
            int type = scanner.nextInt();
            if (type == 1) {
                int x = scanner.nextInt();
                queue.enqueue(x);
            } else if (type == 2) {
                queue.dequeue();
            } else if (type == 3) {
                System.out.println(queue.peek());
            }
        }
        scanner.close();
    }

  • janvenyong
     + 0 comments

    JS

    Barely able to pass without the timeout error after trying multiple times:

    function processData(input) {
    let s1 = [], s2 = []
    let inputs = input.split('\n')
    for (let i = 1; i < inputs.length; i++) {
        let arr = inputs[i].split(' ')
        switch (arr[0]) {
            case '1': {
                s1.push(arr[1])
                break
            }
            case '2': {
                while (s1.length > 0) s2.push(s1.pop())
                s2.pop()
                while (s2.length > 0) s1.push(s2.pop())
                break
            }
            case '3': {
                console.log(s1[0])
                break
            }
        }
    }
}

  • yemengchen4371
     + 0 comments

    Java8 Straightforward and best time-complexity solution:

    import java.io.*;
import java.util.*;

public class Solution {
    private static Scanner scanner = new Scanner(System.in);
    private static Stack<Integer> s1 = new Stack<Integer>();
    private static Stack<Integer> s2 = new Stack<Integer>();
    private static void enqueue(int value){
            s1.push(value);
        }
        
    private static void dequeue(){
            if (s2.isEmpty() == true){
                while (s1.isEmpty() == false){
                    int toS2 = s1.pop();
                    s2.push(toS2);
                }
            }
            int returnValue = s2.pop();
        }
        
    private static void peak(){
            if (s2.isEmpty() == true){
                while (s1.isEmpty() == false){
                    int toS2 = s1.pop();
                    s2.push(toS2);
                }
            }
            System.out.println(s2.peek());
        }

    public static void main(String[] args) {
        /* Enter your code here. Read input from STDIN. Print output to STDOUT. Your class should be named Solution. */
        int total = scanner.nextInt();
        for (int i = 0; i < total; i++) {
            int type = scanner.nextInt();
            if (type == 1){
                enqueue(scanner.nextInt());
            }
            else if (type == 2){
                dequeue();
            }
            else if (type == 3){
                peak();
            }
        }
        
        
        
        
    }
}