题解 | 【模板】队列

package main

import (
	"fmt"
)

type node struct {
	val  int
	next *node
}

type Queue struct {
	head *node
	tail *node
}

func NewQueue() *Queue {
	return &Queue{}
}

func (q *Queue) push(val int) {
	n := &node{val: val, next: nil}
	if q.head == nil {
		q.head = n
		q.tail = q.head
	} else {
		q.tail.next = n
		q.tail = n
	}
}

func (q *Queue) pop() (int, bool) {
	if q.head == nil {
		return 0, false
	} else {
		val := q.head.val
		q.head = q.head.next
		if q.head == nil {
			q.tail = nil
		}
		return val, true
	}
}

func (q *Queue) front() (int, bool) {
	if q.head == nil {
		return 0, false
	} else {
		return q.head.val, true
	}
}

func main() {
	var operation string
	var num int
	q := NewQueue()
	for {
		n, _ := fmt.Scan(&operation)
		if n == 0 {
			break
		} else {
			switch operation {
			case "push":
				_, _ = fmt.Scan(&num)
				q.push(num)
			case "pop":
				val, ok := q.pop()
				if ok {
					fmt.Println(val)
				} else {
					fmt.Println("error")
				}
			case "front":
				val, ok := q.front()
				if ok {
					fmt.Println(val)
				} else {
					fmt.Println("error")
				}
			}
		}
	}
}