using System;

    using System.Collections;

    using System.Collections.Generic;

​

    public class Program

    {

        public void Main()

        {

            var lst = new List<int>(){

                1,

                10,

                7

            };      

            var result = FindNumber(lst);

            result.ForEach(item => {

                Console.WriteLine(string.Format("pre: {0} k: {1} next: {2}",item.pre,item.k,item.next));

            });         

        }

​

        private List<findNumber> FindNumber(List<int> lstInt){

​

            List<findNumber> arrLst = new List<findNumber>();

            lstInt.ForEach(item => {                

                findNumber lst= new findNumber{

                pre=SoChinhPhuongPre((int)item),

                k=item,

                next=SoChinhPhuongNext((int)item)

            };

            arrLst.Add(lst);    

            });             

            return arrLst;

        }   

​

        private int SoChinhPhuongPre(int num){  

            int result=0;

            do {                

                int sqr = (int)Math.Sqrt(num--);                

                if(Math.Pow(sqr,2) == num){                     

                    return num;     

                };

            }while(num>0);

            return result;

        }

        private int SoChinhPhuongNext(int num){ 

            int result=1;

            do {                            

                int sqr = (int)Math.Sqrt(num);              

                if(Math.Pow(sqr,2) == num){                     

                    return num;     

                };

                num++;

            }while(num>1);

            return result;

        }

    }

​

    public class findNumber{

        public int pre{get;set;}

        public int k{get;set;}

        public int next{get;set;}

    }