如何在 Visual C# 中获取数组中第二大的数字？

Question

I have an array of ints. I want to get the second highest number in that array. Is there an easy way to do this?

Answer 1

Try this (using LINQ):

int secondHighest = (from number in numbers
                     orderby number descending
                     select number).Skip(1).First();

Answer 2

You could sort the array and choose the item at the second index, but the following O(n) loop will be much faster.

int[] myArray = new int[] { 0, 1, 2, 3, 13, 8, 5 };
int largest = int.MinValue;
int second = int.MinValue;
foreach (int i in myArray)
{
    if (i > largest)
    {
        second = largest;
        largest = i;
    }
    else if (i > second)
        second = i;
}

System.Console.WriteLine(second);

Answer 3

是的，让2个变数（第一个和第二个）通过数组，每次通过这两个单元格来补偿您得到的结果（始终将最高的放在第一个，第二个最高的放在第二个）一次，您将在第二个上获得第二个变种

Answer 4

You don't specify if you want to do this with the minimum complexity.

Assuming your array is unsorted, please see: How to find the kth largest element in an unsorted array of length n in O(n)?

To find Kth largest element in an unsorted array: Build a max heap in O(n). Now remove k elements from the heap; where each removal costs log(n) time to maintain the heap. Total time complexity = O(n + klogn)

To understand building Max heap in O(n) see Binary heap

Answer 5

max1=0;
max2=0;

for( int i=0; i < a.Length; i++)
{
    if (arr[i]> max1)
    {
        max2=max1;
        max1=arr[i];
    }
    else
    {
       if (a[i]!= max1) && ( a[i] > max2)
          max2[i]=arr[i];
    }
}

Answer 6

Getting the max number first, once the max is changed do a comparison against the second high number to see if it needs to swapped. The second if statement checks if the value is less than the max and is greater than the second highest value. Because of the short circuit, if the first condition fails then it exits the if and skips

    static void Main(string[] args)
    {
        //int[] arr = new int[10] { 9, 4, 6, 2, 11, 100, 53, 23, 72, 81 };
        int[] arr = { 1, 8, 4, 5, 12, 2, 5, 6, 7, 1, 90, 100, 56, 8, 34 };
        int MaxNum = 0;
        int SecNum = 0;
        for (int i = 0; i < arr.Length; i++)
        {
            if (arr[i] > MaxNum)
            {
                if (MaxNum > SecNum) { SecNum = MaxNum; }
                MaxNum = arr[i];
            }

            if (arr[i] < MaxNum && arr[i] > SecNum)
            {
                SecNum = arr[i];
            }
        }

        Console.WriteLine("Highest Num: {0}. Second Highest Num {1}.", MaxNum, SecNum);
        Console.ReadLine();
    }

Answer 7

    int[] myArray = new int[] { 0, 1, 2, 3, 13, 8, 5 };
    int num1=0, temp=0;
    for (int i = 0; i < myArray.Length; i++)
    {
        if (myArray[i] >= num1)
        {
            num1 = myArray[i];
        }
        else if ((myArray[i] < num1) && (myArray[i] > temp))
        {
            temp = myArray[i];
        }
    }
    Console.WriteLine("The Largest Number is: " + num1);
    Console.WriteLine("The Second Highest Number is: " + temp);

Answer 8

int[] arr = { 1, 8, 4, 5, 12, 2, 5, 6, 7, 1, 90, 100, 56, 8, 34 };

int first, second;
// Assuming the array has at least one element:
first = second = arr[0];
for(int i = 1; i < arr.Length; ++i)
{
  if (first < arr[i])
  {
    // 'first' now contains the 2nd largest number encountered thus far:
    second = first;
    first = arr[i];
  }

}
MessageBox.Show(second.ToString());

Answer 9

    static void Main(string[] args)
    {
        int[] myArray = new int[] { 0, 1, 2, 3, 13, 8, 5,12,11,14 };
        int num1 = 0, temp = 0;
        for (int i = 0; i < myArray.Length; i++)
        {
            if (myArray[i] >= num1)
            {
                temp = num1;
                num1 = myArray[i];
            }
            else if ((myArray[i] < num1) && (myArray[i] > temp))
            {
                temp = myArray[i];
            }
        }
        Console.WriteLine("The Largest Number is: " + num1);
        Console.WriteLine("The Second Highest Number is: " + temp);
        Console.ReadKey();
    }

Answer 10

There are two possibilities to find second highest number from an array.

1). Find second max number from an array.

int[] myArray = { 0, 2, 3, 8, 13};

int max = 0;
int second_max = 0;
foreach (int arr in myArray) {
    if (arr > max)
    {
        second_max = max;
        max = arr;
    }
}
Console.WriteLine("First highest number is: "+max);
Console.WriteLine("Second highest number is: " + second_max);

2). Find second max number with the smallest complexity from an array.

int[] myArray = { 0, 2, 3, 13, 8}; //smaller number is given after larger number

int max = 0;
    int second_max = 0;
    foreach (int arr in myArray) {
        if (arr > max)
        {
            second_max = max;
            max = arr;
        }
        else if (arr > second_max)
        {
            second_max = arr;
        }
    }
    Console.WriteLine("First highest number is: "+max);
    Console.WriteLine("Second highest number is: " + second_max);