C++ Program for Mean of range in array
Last Updated :
31 May, 2022
Given an array of n integers. You are given q queries. Write a program to print the 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++
#include <bits/stdc++.h>
using namespace std;
int findMean( int arr[], int l, int r)
{
int sum = 0, count = 0;
for ( int i = l; i <= r; i++) {
sum += arr[i];
count++;
}
int mean = floor (sum / count);
return mean;
}
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;
}
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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++
#include <bits/stdc++.h>
#define MAX 1000005
using namespace std;
int prefixSum[MAX];
void calculatePrefixSum( int arr[], int n)
{
prefixSum[0] = arr[0];
for ( int i = 1; i < n; i++)
prefixSum[i] = prefixSum[i - 1] + arr[i];
}
int findMean( int l, int r)
{
if (l == 0)
return floor (prefixSum[r]/(r+1));
return floor ((prefixSum[r] -
prefixSum[l - 1]) / (r - l + 1));
}
int 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;
}
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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.
Please refer complete article on Mean of range in array for more details!
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