Python3 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.
Python3
import math
def findMean(arr, l, r):
sum , count = 0 , 0
for i in range (l, r + 1 ):
sum + = arr[i]
count + = 1
mean = math.floor( sum / count)
return mean
arr = [ 1 , 2 , 3 , 4 , 5 ]
print (findMean(arr, 0 , 2 ))
print (findMean(arr, 1 , 3 ))
print (findMean(arr, 0 , 4 ))
|
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).
Python3
import math as mt
MAX = 1000005
prefixSum = [ 0 for i in range ( MAX )]
def calculatePrefixSum(arr, n):
prefixSum[ 0 ] = arr[ 0 ]
for i in range ( 1 ,n):
prefixSum[i] = prefixSum[i - 1 ] + arr[i]
def findMean(l, r):
if (l = = 0 ):
return mt.floor(prefixSum[r] / (r + 1 ))
return (mt.floor((prefixSum[r] -
prefixSum[l - 1 ]) /
(r - l + 1 )))
arr = [ 1 , 2 , 3 , 4 , 5 ]
n = len (arr)
calculatePrefixSum(arr, n)
print (findMean( 0 , 2 ))
print (findMean( 1 , 3 ))
print (findMean( 0 , 4 ))
|
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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