最大化给定数组中大小为 K 的子序列中不同元素的计数

给定一个包含N个整数的数组arr[]和一个整数K ，任务是找到K个整数的所有子序列中不同元素的最大计数。

例子：

Input: arr[]={1, 1, 2, 2}, K=3
Output: 2
Explanation: The subsequence {1, 1, 2} has 3 integers and the number of distinct integers in it are 2 which is the maximum possible. Other possible subsequence is {1, 2, 2}.

Input: arr[]={1, 2, 3, 4}, K=3
Output: 3

方法：给定的问题可以使用贪婪的方法来解决，通过观察所需的答案是给定数组或 K 中唯一元素的计数的最小值。现在，要解决这个问题，请按照以下步骤操作：

1. 创建一个集合S ，它存储数组arr[]中存在的不同整数。
2. 遍历数组arr[]并将每个数字插入集合S中。
3. 返回K的最小值和S的大小，这是所需的答案。

下面是上述方法的实现：

C++

// C++ code for the above approach
#include 
using namespace std;
 
// Function to find count of maximum
// distinct elements in a subsequence
// of size K of the given array arr[]
int maxUnique(vector& arr, int K)
{
    // Set data structure to
    // store the unique elements
    unordered_set S;
 
    // Loop to traverse the given array
    for (auto x : arr) {
 
        // Insert into the set
        S.insert(x);
    }
 
    // Returning the minimum out of the two
    return min(K, (int)S.size());
}
 
// Driver Code
int main()
{
    vector arr = { 1, 1, 2, 2 };
    int K = 3;
    cout << maxUnique(arr, K);
}

Java

// Java code for the above approach
import java.util.*;
 
class GFG{
 
// Function to find count of maximum
// distinct elements in a subsequence
// of size K of the given array arr[]
static int maxUnique(int []arr, int K)
{
   
    // Set data structure to
    // store the unique elements
    HashSet S = new HashSet();
 
    // Loop to traverse the given array
    for (int x : arr) {
 
        // Insert into the set
        S.add(x);
    }
 
    // Returning the minimum out of the two
    return Math.min(K, (int)S.size());
}
 
// Driver Code
public static void main(String[] args)
{
    int[] arr = { 1, 1, 2, 2 };
    int K = 3;
    System.out.print(maxUnique(arr, K));
}
}
 
// This code is contributed by 29AjayKumar

Python3

# Python Program to implement
# the above approach
 
# Function to find count of maximum
# distinct elements in a subsequence
# of size K of the given array arr[]
def maxUnique(arr, K):
 
    # Set data structure to
    # store the unique elements
    S = set()
 
    # Loop to traverse the given array
    for x in arr:
 
        # Insert into the set
        S.add(x)
 
    # Returning the minimum out of the two
    return min(K, len(S))
 
# Driver Code
arr = [1, 1, 2, 2]
K = 3
print(maxUnique(arr, K))
 
# This code is contributed by gfgking

C#

// C# implementation for the above approach
using System;
using System.Collections;
using System.Collections.Generic;
 
class GFG
{
 
// Function to find count of maximum
// distinct elements in a subsequence
// of size K of the given array arr[]
static int maxUnique(int []arr, int K)
{
    // Set data structure to
    // store the unique elements
    HashSet S = new HashSet();
 
    // Loop to traverse the given array
    foreach (int x in arr) {
 
        // Insert into the set
        S.Add(x);
    }
 
    // Returning the minimum out of the two
    return Math.Min(K, (int)S.Count);
}
 
// Driver Code
public static void Main()
{
    int []arr = { 1, 1, 2, 2 };
    int K = 3;
    Console.Write(maxUnique(arr, K));
}
}
 
// This code is contributed by Samim Hossain Mondal.

Javascript

 
     // JavaScript Program to implement
     // the above approach
 
     // Function to find count of maximum
     // distinct elements in a subsequence
     // of size K of the given array arr[]
     function maxUnique(arr, K)
     {
      
         // Set data structure to
         // store the unique elements
         let S = new Set();
 
         // Loop to traverse the given array
         for (let x of arr) {
 
             // Insert into the set
             S.add(x);
         }
 
         // Returning the minimum out of the two
         return Math.min(K, S.size);
     }
 
     // Driver Code
     let arr = [1, 1, 2, 2];
     let K = 3;
     document.write(maxUnique(arr, K));
 
 // This code is contributed by Potta Lokesh
 

输出

2

时间复杂度： O(N)
辅助空间： O(N)