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📜  由给定 N 个整数形成的所有对的成对差的平均值

📅  最后修改于: 2022-05-13 01:56:07.879000             🧑  作者: Mango

由给定 N 个整数形成的所有对的成对差的平均值

给定一个包含N个整数的数组arr[] ,任务是计算由给定N个整数形成的两个元素之间的差的平均值

例子:

方法:这个问题可以通过使用贪心方法和前缀和方法来解决。如果数组arr[]中的点按排序顺序排列,则第 i点到所有较大点的距离之和可以计算为: (arr[i+1] – arr[i]) + (arr[ i+2] – arr[i]) … + (arr[N-1] – arr[i]) => (arr[i+1] + arr[i+2]… + arr[N-1]) – arr[i] * (N – 1 – i) 。使用此观察,可以使用以下步骤解决给定问题:

  • 最初以非递减顺序对数组arr[]进行排序。
  • 创建数组arr[]的前缀和数组pre[ ] 。
  • 遍历每个索引i并将(pre[N – 1] – pre[i]) – arr[i] * (N – 1 – i)添加到变量ans中。
  • 所需的答案是ans / count of pairs => ans / (N*(N-1)/2)

下面是上述方法的实现:

C++
// C++ program for above approach
#include 
using namespace std;
 
// Function to find average distance
// between given points on a line
long double averageDistance(
  vector arr, int N)
{
    // Sorting the array arr[]
    sort(arr.begin(), arr.end());
 
    // Stores the prefix sum
    // array of arr[]
    int pre[N] = { 0 };
    pre[0] = arr[0];
 
    // Loop to calculate prefix sum
    for (int i = 1; i < N; i++) {
        pre[i] = pre[i - 1] + arr[i];
    }
 
    // Initialising the answer variable
    long double ans = 0;
 
    // Loop to iterate through arr[]
    for (int i = 0; i < N - 1; i++) {
 
        // Adding summation of all
        // distances from ith point
        ans += (pre[N - 1] - pre[i])
          - arr[i] * (N - 1 - i);
    }
 
    // Return Average
    return ans / ((N * (N - 1)) / 2);
}
 
// Driver Code
int main()
{
    vector arr = { -1, 3, -5, 4 };
    cout << averageDistance(arr, arr.size());
 
    return 0;
}


Java
// Java implementation for the above approach
import java.util.*;
class GFG {
 
    // Function to find average distance
    // between given points on a line
    static double averageDistance(int[] arr, int N)
    {
        // Sorting the array arr[]
        Arrays.sort(arr);
 
        // Stores the prefix sum
        // array of arr[]
        int[] pre = new int[N];
        pre[0] = arr[0];
 
        // Loop to calculate prefix sum
        for (int i = 1; i < N; i++) {
            pre[i] = pre[i - 1] + arr[i];
        }
 
        // Initialising the answer variable
        double ans = 0;
 
        // Loop to iterate through arr[]
        for (int i = 0; i < N - 1; i++) {
 
            // Adding summation of all
            // distances from ith point
            ans += (pre[N - 1] - pre[i])
                   - arr[i] * (N - 1 - i);
        }
 
        // Return Average
        ans = (ans / ((N * (N - 1)) / 2));
        return ans;
    }
 
    // Driver Code
    public static void main(String[] args)
    {
        int[] arr = { -1, 3, -5, 4 };
 
        System.out.print(String.format(
            "%.5f", averageDistance(arr, arr.length)));
    }
}
 
// This code is contributed by ukasp.


Python3
# Python3 program for above approach
 
# Function to find average distance
# between given points on a line
def averageDistance(arr, N):
     
    # Sorting the array arr[]
    arr.sort()
 
    # Stores the prefix sum
    # array of arr[]
    pre = [0 for _ in range(N)]
    pre[0] = arr[0]
 
    # Loop to calculate prefix sum
    for i in range(1, N):
        pre[i] = pre[i - 1] + arr[i]
 
    # Initialising the answer variable
    ans = 0
 
    # Loop to iterate through arr[]
    for i in range(0, N - 1):
         
        # Adding summation of all
        # distances from ith point
        ans += ((pre[N - 1] - pre[i]) -
               (arr[i] * (N - 1 - i)))
 
    # Return Average
    return ans / ((N * (N - 1)) / 2)
 
# Driver Code
if __name__ == "__main__":
 
    arr = [ -1, 3, -5, 4 ]
     
    print(averageDistance(arr, len(arr)))
 
# This code is contributed by rakeshsahni


C#
// C# implementation for the above approach
using System;
class GFG
{
 
// Function to find average distance
// between given points on a line
static double averageDistance(
  int []arr, int N)
{
    // Sorting the array arr[]
    Array.Sort(arr);
 
    // Stores the prefix sum
    // array of arr[]
    int []pre = new int[N];
    pre[0] = arr[0];
 
    // Loop to calculate prefix sum
    for (int i = 1; i < N; i++) {
        pre[i] = pre[i - 1] + arr[i];
    }
 
    // Initialising the answer variable
    double ans = 0;
 
    // Loop to iterate through arr[]
    for (int i = 0; i < N - 1; i++) {
 
        // Adding summation of all
        // distances from ith point
        ans += (pre[N - 1] - pre[i])
          - arr[i] * (N - 1 - i);
    }
 
    // Return Average
    ans  = Math.Round((ans / ((N * (N - 1)) / 2)), 5);
    return ans;
}
 
// Driver Code
public static void Main()
{
    int []arr = { -1, 3, -5, 4 };
     
    Console.Write(averageDistance(arr, arr.Length));
}
}
 
// This code is contributed by Samim Hossain Mondal.


Javascript


输出
5.16667

时间复杂度: O(N*log N)
辅助空间: O(1)