夜过吊桥算法

Posted 2020-08-06

问题描述：五个人打算过一座吊桥，开始时他们都位于该桥的一侧。天很黑，五个人手里只有一个手电筒。该桥一次最多只能同时过两个人，无论是一个人还是两个人过桥，都需要携带手电筒看路。而且手电筒只能通过人携带过桥的方式传递。第一个人过桥需要1分钟时间，第二个人过桥需要2分钟，第三个人需要5分钟，第四个需要7分钟，第五个需要10分钟。由于速度不同，两个人一起过桥的话，速度以慢的人为准。求最快过桥时间。

Main

using System;
using System.Collections.Generic;
using System.Linq;

namespace PassRiver
{
    class Program
    {
        private const int maxPassTogetherCount = 2;
        static void Main(string[] args)
        {
            List<Person> leftPersons = new List<Person>();
            List<Person> rightPersons = new List<Person>();
            Person p1 = new Person(1);
            Person p2 = new Person(2);
            Person p3 = new Person(5);
            Person p4 = new Person(7);
            Person p5 = new Person(10);

            leftPersons.Add(p4);
            leftPersons.Add(p5);
            leftPersons.Add(p1);
            leftPersons.Add(p2);
            leftPersons.Add(p3);

            int totalTime = 0;

            while (leftPersons.Count != 0)
            {
                List<Person> twoFastSpeedPersons = FindTwoFastSpeedPersons(leftPersons);
                foreach (Person person in twoFastSpeedPersons)
                {
                    leftPersons.Remove(person);
                }
                rightPersons.AddRange(twoFastSpeedPersons);
                if (twoFastSpeedPersons.Count > 1)
                {
                    totalTime += twoFastSpeedPersons[1].Speed;
                }
                else if (twoFastSpeedPersons.Count == 1)
                {
                    totalTime += twoFastSpeedPersons[0].Speed;  
                }
                else
                {
                    
                }
                //-------------
                Console.WriteLine("---Go To Right---------->");
                foreach (Person person in twoFastSpeedPersons)
                {
                    Console.WriteLine(person.Speed);
                }
                Console.WriteLine("Total Time:" + totalTime);
                Console.WriteLine();
                //-------------

                if (leftPersons.Count == 0 || rightPersons.Count==5)
                {
                    break;
                }



                Person fastSpeedPerson = FindFastSpeedPerson(rightPersons);
                rightPersons.Remove(fastSpeedPerson);
                leftPersons.Add(fastSpeedPerson);
                totalTime += fastSpeedPerson.Speed;
                //-------------
                Console.WriteLine("<----------Go Back Left---");
                Console.WriteLine(fastSpeedPerson.Speed);
                Console.WriteLine("Total Time:" + totalTime);
                Console.WriteLine();
                //-------------
                if (leftPersons.Count == 0 || rightPersons.Count == 5)
                {
                    break;
                }
                

                List<Person> twoLowestSpeedPersons = FindTwoLowestSpeedPersons(leftPersons);
                foreach (Person person in twoLowestSpeedPersons)
                {
                    leftPersons.Remove(person);
                }
                rightPersons.AddRange(twoLowestSpeedPersons);
                totalTime += twoLowestSpeedPersons[0].Speed;
                //-------------
                Console.WriteLine("---Go To Right---------->");
                foreach (Person person in twoLowestSpeedPersons)
                {
                    Console.WriteLine(person.Speed);
                }
                Console.WriteLine("Total Time:" + totalTime);
                Console.WriteLine();
                //-------------
                if (leftPersons.Count == 0 || rightPersons.Count == 5)
                {
                    break;
                }

                fastSpeedPerson = FindFastSpeedPerson(rightPersons);
                rightPersons.Remove(fastSpeedPerson);
                leftPersons.Add(fastSpeedPerson);
                totalTime += fastSpeedPerson.Speed;
                //-------------
                Console.WriteLine("<----------Go Back Left---");
                Console.WriteLine(fastSpeedPerson.Speed);
                Console.WriteLine("totalTime:" + totalTime);
                Console.WriteLine();
                //-------------
                if (leftPersons.Count == 0 || rightPersons.Count == 5)
                {
                    break;
                }
            }

            Console.WriteLine("------------Total Time-------------");
            Console.WriteLine(totalTime);

            Console.ReadKey();

        }

        public static List<Person> FindTwoLowestSpeedPersons(List<Person> persons)
        {
            List<Person> sortedPersons = persons.OrderByDescending(s => s.Speed).ToList();
            List<Person> passedPersons = new List<Person>();

            if (persons.Count > 1)
            {
                
                passedPersons = new List<Person>();
                passedPersons.Add(sortedPersons[0]);
                passedPersons.Add(sortedPersons[1]);  
            }
            else if (persons.Count == 1)
            {
                passedPersons.Add(sortedPersons[0]);
            }
            else
            {
                
            }

            return passedPersons;
        }

        public static List<Person> FindTwoFastSpeedPersons(List<Person> persons)
        {
            List<Person> sortedPersons = persons.OrderBy(s => s.Speed).ToList();
            List<Person> passedPersons = new List<Person>();

            if (persons.Count > 1)
            {
                
                passedPersons = new List<Person>();
                passedPersons.Add(sortedPersons[0]);
                passedPersons.Add(sortedPersons[1]);
            }
            else if (persons.Count == 1)
            {
                passedPersons.Add(sortedPersons[0]);
            }
            else
            {
                return null;
            }

            return passedPersons;
        }

        public static Person FindFastSpeedPerson(List<Person> persons)
        {
            if (persons.Count > 0)
            {
                List<Person> sortedPersons = persons.OrderBy(s => s.Speed).ToList();
                return sortedPersons[0];
            }
            else
            {
                return null;
            }
        }

        
    }
}

 

Person

namespace PassRiver
{
    public class Person
    {
        private int _speed;
        private Side _side;

        public Person(int speed)
        {
            _speed = speed;
            _side = Side.Left;
        }

        public int Speed
        {
            get { return _speed; }

            set { _speed = value; }
        }

        public Side Side
        {
            get { return _side; }

            set { _side = value; }
        }
    }
}

 

Side

namespace PassRiver
{
    public enum Side
    {
        Left = 0,
        Right = 1
    }
}

 

SortUtil

using System.Collections.Generic;

namespace PassRiver
{
    public static class SortUtil
    {
        public static List<Person> BubbleSort(List<Person> persons)
        {
            for (int i = 0; i < persons.Count - 1; i++)
            {
                for (int j = i + 1; j < persons.Count; j++)
                {
                    if (persons[i].Speed < persons[j].Speed)
                    {
                        Person temp = persons[j];
                        persons[j] = persons[i];
                        persons[i] = temp;
                    }
                }
            }

            return persons;
        }
    }
}