Mean of range in array

31 May, 2022
Given an array of n integers. You are given q queries. Write a program to print floor value of mean in range l to r for each query in a new line.
Examples : 
Input : arr[] = {1, 2, 3, 4, 5}
        q = 3
        0 2
        1 3
        0 4
Output : 2
         3
         3
Here for 0 to 2 (1 + 2 + 3) / 3 = 2

Input : arr[] = {6, 7, 8, 10}
        q = 2
        0 3
        1 2
Output : 7
         7
Naive Approach: We can run loop for each query l to r and find sum and number of elements in range. After this we can print floor of mean for each query.  
C++
C
Java
Python3
C#
PHP
Javascript
// CPP program to find floor value// of mean in range l to r#include <bits/stdc++.h>using namespace std; // To find mean of range in l to rint findMean(int arr[], int l, int r){    // Both sum and count are    // initialize to 0    int sum = 0, count = 0;     // To calculate sum and number    // of elements in range l to r    for (int i = l; i <= r; i++) {        sum += arr[i];        count++;    }     // Calculate floor value of mean    int mean = floor(sum / count);     // Returns mean of array    // in range l to r    return mean;} // Driver program to test findMean()int main(){    int arr[] = { 1, 2, 3, 4, 5 };    cout << findMean(arr, 0, 2) << endl;    cout << findMean(arr, 1, 3) << endl;    cout << findMean(arr, 0, 4) << endl;    return 0;}
// C program to find floor value// of mean in range l to r#include <stdio.h>#include <math.h> // To find mean of range in l to rint findMean(int arr[], int l, int r){    // Both sum and count are    // initialize to 0    int sum = 0, count = 0;     // To calculate sum and number    // of elements in range l to r    for (int i = l; i <= r; i++) {        sum += arr[i];        count++;    }     // Calculate floor value of mean    int mean = floor(sum / count);     // Returns mean of array    // in range l to r    return mean;} // Driver program to test findMean()int main(){    int arr[] = { 1, 2, 3, 4, 5 };    printf("%d\n",findMean(arr, 0, 2));    printf("%d\n",findMean(arr, 1, 3));    printf("%d\n",findMean(arr, 0, 4));    return 0;} // This code is contributed by kothavvsaakash
// Java program to find floor value// of mean in range l to rpublic class Main {     // To find mean of range in l to r    static int findMean(int arr[], int l, int r)    {        // Both sum and count are        // initialize to 0        int sum = 0, count = 0;         // To calculate sum and number        // of elements in range l to r        for (int i = l; i <= r; i++) {            sum += arr[i];            count++;        }         // Calculate floor value of mean        int mean = (int)Math.floor(sum / count);         // Returns mean of array        // in range l to r        return mean;    }     // Driver program to test findMean()    public static void main(String[] args)    {        int arr[] = { 1, 2, 3, 4, 5 };        System.out.println(findMean(arr, 0, 2));        System.out.println(findMean(arr, 1, 3));        System.out.println(findMean(arr, 0, 4));    }}
# Python 3 program to find floor value# of mean in range l to rimport math # To find mean of range in l to rdef findMean(arr, l, r):         # Both sum and count are    # initialize to 0    sum, count = 0, 0         # To calculate sum and number    # of elements in range l to r    for i in range(l, r + 1):        sum += arr[i]        count += 1     # Calculate floor value of mean    mean = math.floor(sum / count)     # Returns mean of array    # in range l to r    return mean # Driver Codearr = [ 1, 2, 3, 4, 5 ]     print(findMean(arr, 0, 2))print(findMean(arr, 1, 3))print(findMean(arr, 0, 4)) # This code is contributed# by PrinciRaj1992
//C# program to find floor value// of mean in range l to rusing System; public class GFG {      // To find mean of range in l to r    static int findMean(int []arr, int l, int r)    {        // Both sum and count are        // initialize to 0        int sum = 0, count = 0;          // To calculate sum and number        // of elements in range l to r        for (int i = l; i <= r; i++) {            sum += arr[i];            count++;        }          // Calculate floor value of mean        int mean = (int)Math.Floor((double)sum / count);          // Returns mean of array        // in range l to r        return mean;    }      // Driver program to test findMean()    public static void Main()    {        int []arr = { 1, 2, 3, 4, 5 };        Console.WriteLine(findMean(arr, 0, 2));        Console.WriteLine(findMean(arr, 1, 3));        Console.WriteLine(findMean(arr, 0, 4));    }} /*This code is contributed by PrinciRaj1992*/
<?php// PHP program to find floor// value of mean in range l to r // To find mean of// range in l to rfunction findMean($arr, $l, $r){    // Both sum and count    // are initialize to 0    $sum = 0;    $count = 0;     // To calculate sum and    // number of elements in    // range l to r    for ($i = $l; $i <= $r; $i++)    {        $sum += $arr[$i];        $count++;    }     // Calculate floor    // value of mean    $mean = floor($sum / $count);     // Returns mean of array    // in range l to r    return $mean;} // Driver Code$arr = array(1, 2, 3, 4, 5);echo findMean($arr, 0, 2), "\n";echo findMean($arr, 1, 3), "\n";echo findMean($arr, 0, 4), "\n"; // This code is contributed by ajit?>
<script>    // Javascript program to find floor value    // of mean in range l to r         // To find mean of range in l to r    function findMean(arr, l, r)    {        // Both sum and count are        // initialize to 0        let sum = 0, count = 0;            // To calculate sum and number        // of elements in range l to r        for (let i = l; i <= r; i++) {            sum += arr[i];            count++;        }            // Calculate floor value of mean        let mean = Math.floor(sum / count);            // Returns mean of array        // in range l to r        return mean;    }         let arr = [ 1, 2, 3, 4, 5 ];    document.write(findMean(arr, 0, 2) + "</br>");    document.write(findMean(arr, 1, 3) + "</br>");    document.write(findMean(arr, 0, 4) + "</br>"); </script>
Output : 
2
3
3
Time complexity: O(n*q) where q is the number of queries and n is the size of the array. Here in the above code q is 3 as the findMean function is used 3 times.Auxiliary Space: O(1)
Efficient Approach: We can find sum of numbers using numbers using prefix sum. The prefixSum[i] denotes the sum of first i elements. So sum of numbers in range l to r will be prefixSum[r] – prefixSum[l-1]. Number of elements in range l to r will be r – l + 1. So we can now print mean of range l to r in O(1). 
C++
Java
Python3
C#
Javascript
C
// CPP program to find floor value// of mean in range l to r#include <bits/stdc++.h>#define MAX 1000005using namespace std; int prefixSum[MAX]; // To calculate prefixSum of arrayvoid calculatePrefixSum(int arr[], int n){    // Calculate prefix sum of array    prefixSum[0] = arr[0];    for (int i = 1; i < n; i++)        prefixSum[i] = prefixSum[i - 1] + arr[i];} // To return floor of mean// in range l to rint findMean(int l, int r){    if (l == 0)      return floor(prefixSum[r]/(r+1));     // Sum of elements in range l to    // r is prefixSum[r] - prefixSum[l-1]    // Number of elements in range    // l to r is r - l + 1    return floor((prefixSum[r] -          prefixSum[l - 1]) / (r - l + 1));} // Driver program to test above functionsint main(){    int arr[] = { 1, 2, 3, 4, 5 };    int n = sizeof(arr) / sizeof(arr[0]);    calculatePrefixSum(arr, n);    cout << findMean(0, 2) << endl;    cout << findMean(1, 3) << endl;    cout << findMean(0, 4) << endl;    return 0;}
// Java program to find floor value// of mean in range l to rpublic class Main {public static final int MAX = 1000005;    static int prefixSum[] = new int[MAX];     // To calculate prefixSum of array    static void calculatePrefixSum(int arr[], int n)    {        // Calculate prefix sum of array        prefixSum[0] = arr[0];        for (int i = 1; i < n; i++)            prefixSum[i] = prefixSum[i - 1] + arr[i];    }     // To return floor of mean    // in range l to r    static int findMean(int l, int r)    {        if (l == 0)           return (int)Math.floor(prefixSum[r] / (r + 1));                 // Sum of elements in range l to        // r is prefixSum[r] - prefixSum[l-1]        // Number of elements in range        // l to r is r - l + 1        return (int)Math.floor((prefixSum[r] -                prefixSum[l - 1]) / (r - l + 1));    }     // Driver program to test above functions    public static void main(String[] args)    {        int arr[] = { 1, 2, 3, 4, 5 };        int n = arr.length;        calculatePrefixSum(arr, n);        System.out.println(findMean(1, 2));        System.out.println(findMean(1, 3));        System.out.println(findMean(1, 4));    }}
# Python3 program to find floor value# of mean in range l to rimport math as mt MAX = 1000005prefixSum = [0 for i in range(MAX)] # To calculate prefixSum of arraydef calculatePrefixSum(arr, n):     # Calculate prefix sum of array    prefixSum[0] = arr[0]     for i in range(1,n):        prefixSum[i] = prefixSum[i - 1] + arr[i] # To return floor of mean# in range l to rdef findMean(l, r):     if (l == 0):        return mt.floor(prefixSum[r] / (r + 1))     # Sum of elements in range l to    # r is prefixSum[r] - prefixSum[l-1]    # Number of elements in range    # l to r is r - l + 1    return (mt.floor((prefixSum[r] -                      prefixSum[l - 1]) /                          (r - l + 1))) # Driver Codearr = [1, 2, 3, 4, 5] n = len(arr) calculatePrefixSum(arr, n)print(findMean(0, 2))print(findMean(1, 3))print(findMean(0, 4)) # This code is contributed by Mohit Kumar
// C# program to find floor value// of mean in range l to rusing System;                     public class GFG {public static readonly int MAX = 1000005;    static int []prefixSum = new int[MAX];      // To calculate prefixSum of array    static void calculatePrefixSum(int []arr, int n)    {        // Calculate prefix sum of array        prefixSum[0] = arr[0];        for (int i = 1; i < n; i++)            prefixSum[i] = prefixSum[i - 1] + arr[i];    }      // To return floor of mean    // in range l to r    static int findMean(int l, int r)    {        if (l == 0)           return (int)Math.Floor((double)(prefixSum[r] / (r + 1)));                  // Sum of elements in range l to        // r is prefixSum[r] - prefixSum[l-1]        // Number of elements in range        // l to r is r - l + 1        return (int)Math.Floor((double)(prefixSum[r] -                prefixSum[l - 1]) / (r - l + 1));    }      // Driver program to test above functions    public static void Main()    {        int []arr = { 1, 2, 3, 4, 5 };        int n = arr.Length;        calculatePrefixSum(arr, n);        Console.WriteLine(findMean(1, 2));        Console.WriteLine(findMean(1, 3));        Console.WriteLine(findMean(1, 4));    }} //This code is contributed by PrinciRaj1992
<script> // Javascript program to find floor value// of mean in range l to rlet MAX = 1000005;let prefixSum = new Array(MAX);prefixSum.fill(0); // To calculate prefixSum of arrayfunction calculatePrefixSum(arr, n){         // Calculate prefix sum of array    prefixSum[0] = arr[0];    for(let i = 1; i < n; i++)        prefixSum[i] = prefixSum[i - 1] + arr[i];} // To return floor of mean// in range l to rfunction findMean(l, r){    if (l == 0)       return parseInt(Math.floor(prefixSum[r] /                      (r + 1)), 10);          // Sum of elements in range l to    // r is prefixSum[r] - prefixSum[l-1]    // Number of elements in range    // l to r is r - l + 1    return parseInt(Math.floor((prefixSum[r] -                                prefixSum[l - 1]) /                                (r - l + 1)), 10);} // Driver codelet arr = [ 1, 2, 3, 4, 5 ];let n = arr.length;calculatePrefixSum(arr, n); document.write(findMean(1, 2) + "</br>");document.write(findMean(1, 3) + "</br>");document.write(findMean(1, 4) + "</br>"); // This code is contributed by divyeshrabadiya07 </script>
// C program to find floor value// of mean in range l to r#include <stdio.h>#include <math.h> #define MAX 1000005 int prefixSum[MAX]; // To calculate prefixSum of arrayvoid calculatePrefixSum(int arr[], int n){    // Calculate prefix sum of array    prefixSum[0] = arr[0];    for (int i = 1; i < n; i++)        prefixSum[i] = prefixSum[i - 1] + arr[i];} // To return floor of mean// in range l to rint findMean(int l, int r){    if (l == 0)      return floor(prefixSum[r]/(r+1));     // Sum of elements in range l to    // r is prefixSum[r] - prefixSum[l-1]    // Number of elements in range    // l to r is r - l + 1    return floor((prefixSum[r] -          prefixSum[l - 1]) / (r - l + 1));} // Driver program to test above functionsint main(){    int arr[] = { 1, 2, 3, 4, 5 };    int n = sizeof(arr) / sizeof(arr[0]);    calculatePrefixSum(arr, n);    printf("%d\n",findMean(0, 2));    printf("%d\n",findMean(1, 3));    printf("%d\n",findMean(0, 4));    return 0;}
Output: 
2
3
3
Time complexity: O(n+q) where q is the number of queries and n is the size of the array. Here in the above code q is 3 as the findMean function is used 3 times.Auxiliary Space: O(k) where k=1000005.
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