有100万个数字（1到9），其中只有1个数字重复2次，如何快速找出该数字

有100万个数字（1到9），其中只有1个数字重复2次，如何快速找出该数字

rt, C# codes as below:

using System;

using System.Collections.Generic;

namespace ConsoleApp

{

class Program

{

static void Main(string[] args)

{

List<int> list = new List<int>();

for (int i = 1; i < 10; i++)

{

for (int j = 0; j < i; j++)

{

list.Add(i);

}

list.Add(1);

list.Add(1);

}

Console.WriteLine(GetNum(list));

Console.ReadKey();

}

static int GetNum(List<int> listNums)

{

bool[] ifRemoved = new bool[9];

int[] counterTimes = new int[9];

int movedNum = 0;

foreach (int i in listNums)

{

if (i <= 0 || i > 9)

throw new System.FormatException(string.Format("Unexpected num value {0}!", i));

if (ifRemoved[i - 1] == false)

{

counterTimes[i - 1]++;

if (counterTimes[i - 1] > 2)

{

ifRemoved[i - 1] = true;

movedNum++;

if (movedNum == 8)

{

for (int j = 0; j < 9; j++)

{

if (ifRemoved[j] == false)

return j + 1;

}

}

}

}

}

for (int j = 0; j < 9; j++)

{

if (counterTimes[j] == 2)

return j + 1;

}

throw new System.ArgumentException("There is no suitable num in the param array!");

}

}

}