查找数组中最大的三个不同元素

给定一个包含所有不同元素的数组，找到最大的三个元素。预期的时间复杂度为O(n)，额外空间为O(1)。
例子 ：

Input: arr[] = {10, 4, 3, 50, 23, 90}
Output: 90, 50, 23

方法1 –
下面是算法：

1) Initialize the largest three elements as minus infinite.
    first = second = third = -∞

2) Iterate through all elements of array.
   a) Let current array element be x.
   b) If (x > first)
      {
          // This order of assignment is important
          third = second
          second = first
          first = x   
       }
   c)  Else if (x > second)
      {
          third = second
          second = x 
      }
   d)  Else if (x > third)
      {
          third = x  
      }

3) Print first, second and third.

下面是上述算法的实现。

C++

// C++ program for find the largest
// three elements in an array
#include 
using namespace std;
 
// Function to print three largest elements
void print3largest(int arr[], int arr_size)
{
    int first, second, third;
 
    // There should be atleast three elements
    if (arr_size < 3)
    {
        cout << " Invalid Input ";
        return;
    }
 
    third = first = second = INT_MIN;
    for(int i = 0; i < arr_size; i++)
    {
         
        // If current element is
        // greater than first
        if (arr[i] > first)
        {
            third = second;
            second = first;
            first = arr[i];
        }
 
        // If arr[i] is in between first
        // and second then update second
        else if (arr[i] > second)
        {
            third = second;
            second = arr[i];
        }
 
        else if (arr[i] > third)
            third = arr[i];
    }
 
    cout << "Three largest elements are "
        << first << " " << second << " "
        << third << endl;
}
 
// Driver code
int main()
{
    int arr[] = { 12, 13, 1, 10, 34, 1 };
    int n = sizeof(arr) / sizeof(arr[0]);
     
    print3largest(arr, n);
    return 0;
}
 
// This code is contributed by Anjali_Chauhan

C

// C program for find the largest
// three elements in an array
#include  /* For INT_MIN */
#include 
 
/* Function to print three largest elements */
void print3largest(int arr[], int arr_size)
{
    int i, first, second, third;
 
    /* There should be atleast three elements */
    if (arr_size < 3) {
        printf(" Invalid Input ");
        return;
    }
 
    third = first = second = INT_MIN;
    for (i = 0; i < arr_size; i++) {
        /* If current element is greater than first*/
        if (arr[i] > first) {
            third = second;
            second = first;
            first = arr[i];
        }
 
        /* If arr[i] is in between first and second then update second  */
        else if (arr[i] > second) {
            third = second;
            second = arr[i];
        }
 
        else if (arr[i] > third)
            third = arr[i];
    }
 
    printf("Three largest elements are %d %d %d\n", first, second, third);
}
 
/* Driver program to test above function */
int main()
{
    int arr[] = { 12, 13, 1, 10, 34, 1 };
    int n = sizeof(arr) / sizeof(arr[0]);
    print3largest(arr, n);
    return 0;
}
/*This code is edited by Ayush Singla(@ayusin51)*/

Java

// Java code to find largest three elements
// in an array
 
class PrintLargest {
    /* Function to print three largest elements */
    static void print3largest(int arr[], int arr_size)
    {
        int i, first, second, third;
 
        /* There should be atleast three elements */
        if (arr_size < 3) {
            System.out.print(" Invalid Input ");
            return;
        }
 
        third = first = second = Integer.MIN_VALUE;
        for (i = 0; i < arr_size; i++) {
            /* If current element is greater than
            first*/
            if (arr[i] > first) {
                third = second;
                second = first;
                first = arr[i];
            }
 
            /* If arr[i] is in between first and
            second then update second  */
            else if (arr[i] > second) {
                third = second;
                second = arr[i];
            }
 
            else if (arr[i] > third)
                third = arr[i];
        }
 
        System.out.println("Three largest elements are " + first + " " + second + " " + third);
    }
 
    /* Driver program to test above function*/
    public static void main(String[] args)
    {
        int arr[] = { 12, 13, 1, 10, 34, 1 };
        int n = arr.length;
        print3largest(arr, n);
    }
}
/*This code is contributed by Prakriti Gupta
and edited by Ayush Singla(@ayusin51)*/

Python3

# Python3 code to find largest three
# elements in an array
import sys
 
# Function to print three largest
# elements
def print3largest(arr, arr_size):
 
    # There should be atleast three
    # elements
    if (arr_size < 3):
     
        print(" Invalid Input ")
        return
     
    third = first = second = -sys.maxsize
     
    for i in range(0, arr_size):
     
        # If current element is greater
        # than first
        if (arr[i] > first):
         
            third = second
            second = first
            first = arr[i]
         
 
        # If arr[i] is in between first
        # and second then update second
        elif (arr[i] > second):
         
            third = second
            second = arr[i]
         
        elif (arr[i] > third):
            third = arr[i]
     
    print("Three largest elements are",
                  first, second, third)
 
# Driver program to test above function
arr = [12, 13, 1, 10, 34, 1]
n = len(arr)
print3largest(arr, n)
 
# This code is contributed by Smitha Dinesh Semwal
# and edited by Ayush Singla(@ayusin51).

C#

// C# code to find largest
// three elements in an array
using System;
 
class PrintLargest {
 
    // Function to print three
    // largest elements
    static void print3largest(int[] arr,
                              int arr_size)
    {
        int i, first, second, third;
 
        // There should be atleast three elements
        if (arr_size < 3) {
            Console.WriteLine("Invalid Input");
            return;
        }
 
        third = first = second = 000;
        for (i = 0; i < arr_size; i++) {
            // If current element is
            // greater than first
            if (arr[i] > first) {
                third = second;
                second = first;
                first = arr[i];
            }
 
            // If arr[i] is in between first
            // and second then update second
            else if (arr[i] > second) {
                third = second;
                second = arr[i];
            }
 
            else if (arr[i] > third)
                third = arr[i];
        }
 
        Console.WriteLine("Three largest elements are " + first + " " + second + " " + third);
    }
 
    // Driver code
    public static void Main()
    {
        int[] arr = new int[] { 12, 13, 1, 10, 34, 1 };
        int n = arr.Length;
        print3largest(arr, n);
    }
}
 
// This code is contributed by KRV and edited by Ayush Singla(@ayusin51).

PHP

 $first)
        {
            $third = $second;
            $second = $first;
            $first = $arr[$i];
        }
 
        // If arr[i] is in between first
        // and second then update second
        else if ($arr[$i] > $second)
        {
            $third = $second;
            $second = $arr[$i];
        }
 
        else if ($arr[$i] > $third)
            $third = $arr[$i];
    }
 
    echo "Three largest elements are ",
       $first, " ", $second, " ", $third;
}
 
 
// Driver Code
$arr = array(12, 13, 1,
             10, 34, 1);
$n = count($arr);
print3largest($arr, $n);
 
// This code is contributed by anuj_67 and edited by Ayush Singla(@ayusin51).
?>

Javascript

 
// Javascript program for find the largest
// three elements in an array
 
// Function to print three largest elements
function print3largest(arr, arr_size)
{
    let first, second, third;
 
    // There should be atleast three elements
    if (arr_size < 3)
    {
        document.write(" Invalid Input ");
        return;
    }
 
    third = first = second = Number.MIN_VALUE;
    for(let i = 0; i < arr_size; i++)
    {
         
        // If current element is
        // greater than first
        if (arr[i] > first)
        {
            third = second;
            second = first;
            first = arr[i];
        }
 
        // If arr[i] is in between first
        // and second then update second
        else if (arr[i] > second)
        {
            third = second;
            second = arr[i];
        }
 
        else if (arr[i] > third)
            third = arr[i];
    }
 
    document.write("Three largest elements are "
        + first + " " + second + " "
        + third + "<br>");
}
 
// Driver code
    let arr = [ 12, 13, 1, 10, 34, 1 ];
    let n = arr.length;
     
    print3largest(arr, n);
     
// This is code is contributed by Mayank Tyagi
 

输出 ：

Three largest elements are 34 13 12

方法二
解决此问题的有效方法是使用任何O(nLogn)排序算法并简单地返回最后3个最大元素。

C++

// C++ code to find largest
// three elements in an array
#include 
using namespace std;
 
void find3largest(int arr[], int n)
{
    sort(arr, arr + n); // It uses Tuned Quicksort with
    // avg. case Time complexity = O(nLogn)
 
    int check = 0, count = 1;
 
    for (int i = 1; i <= n; i++) {
 
        if (count < 4) {
            if (check != arr[n - i]) {
                // to handle duplicate values
                cout << arr[n - i] << " ";
                check = arr[n - i];
                count++;
            }
        }
        else
            break;
    }
}
 
// Driver code
int main()
{
    int arr[] = { 12, 45, 1, -1, 45, 54, 23, 5, 0, -10 };
    int n = sizeof(arr) / sizeof(arr[0]);
    find3largest(arr, n);
}
 
// This code is contibuted by Rajput-Ji

Java

// Java code to find largest
// three elements in an array
 
import java.io.*;
import java.util.Arrays;
 
class GFG {
    void find3largest(int[] arr)
    {
        Arrays.sort(arr); // It uses Tuned Quicksort with
        // avg. case Time complexity = O(nLogn)
        int n = arr.length;
        int check = 0, count = 1;
 
        for (int i = 1; i <= n; i++) {
 
            if (count < 4) {
                if (check != arr[n - i]) {
                    // to handle duplicate values
                    System.out.print(arr[n - i] + " ");
                    check = arr[n - i];
                    count++;
                }
            }
            else
                break;
        }
    }
 
    // Driver code
    public static void main(String[] args)
    {
        GFG obj = new GFG();
        int[] arr = { 12, 45, 1, -1, 45, 54, 23, 5, 0, -10 };
        obj.find3largest(arr);
    }
}
// This code is contibuted by Prashant Malik

Python3

# Python3 code to find largest
# three elements in an array
def find3largest(arr, n):
    arr = sorted(arr) # It uses Tuned Quicksort with
                      # avg. case Time complexity = O(nLogn)
 
    check = 0
    count = 1
 
    for i in range(1, n + 1):
 
        if(count < 4):
            if(check != arr[n - i]):
                 
                # to handle duplicate values
                print(arr[n - i], end = " ")
                check = arr[n - i]
                count += 1
        else:
            break
 
# Driver code
arr = [12, 45, 1, -1, 45,
       54, 23, 5, 0, -10]
n = len(arr)
find3largest(arr, n)
 
# This code is contibuted by mohit kumar

C＃

// C# code to find largest
// three elements in an array
using System;
 
class GFG {
    void find3largest(int[] arr)
    {
        Array.Sort(arr); // It uses Tuned Quicksort with
        // avg. case Time complexity = O(nLogn)
        int n = arr.Length;
        int check = 0, count = 1;
 
        for (int i = 1; i <= n; i++) {
            if (count < 4) {
                if (check != arr[n - i]) {
                    // to handle duplicate values
                    Console.Write(arr[n - i] + " ");
                    check = arr[n - i];
                    count++;
                }
            }
            else
                break;
        }
    }
 
    // Driver code
    public static void Main()
    {
        GFG obj = new GFG();
        int[] arr = { 12, 45, 1, -1, 45,
                      54, 23, 5, 0, -10 };
        obj.find3largest(arr);
    }
}
 
// This code is contibuted by Code_Mech

Java脚本

 
// JavaScript code to find largest
// three elements in an array
 
     function find3largest(arr) {
        arr.sort((a,b)=>a-b); // It uses Tuned Quicksort with
        // avg. case Time complexity = O(nLogn)
  
        let check = 0, count = 1;
  
        for (let i = 1; i <= arr.length; i++) {
  
            if (count < 4) {
                if (check != arr[arr.length - i]) {
                    // to handle duplicate values
                    document.write(arr[arr.length - i] + " ");
                    check = arr[arr.length - i];
                    count++;
                }
            }
            else
                break;
        }
    }
  
    // Driver code
 
    let arr = [ 12, 45, 1, -1, 45, 54, 23, 5, 0, -10 ];
    find3largest(arr);
  
// This code is contributed by Surbhi Tyagi
 

输出 ：

54 45 23

方法3 –
我们可以使用C++ STL的部分排序。 partial_sort使用Heapselect，对于小型M，它的性能比Quickselect更好。作为副作用，Heapselect的最终状态为您留下了一个堆，这意味着您“免费”获得了Heapsort算法的前半部分。复杂度是“大约” O(N log(M)) ，其中M是距离(中间优先)。

C++

#include 
using namespace std;
int main()
{
    vector V = { 11, 65, 193, 36, 209, 664, 32 };
    partial_sort(V.begin(), V.begin() + 3, V.end(), greater());
 
    cout << "first = " << V[0] << "\n";
    cout << "second = " << V[1] << "\n";
    cout << "third = " << V[2] << "\n";
    return 0;
}

输出 ：

first = 664
second = 209
third = 193