Javascript Program for Mean of range in array
Last Updated :
18 Sep, 2024
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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.
// 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];
console.log(findMean(arr, 0, 2));
console.log(findMean(arr, 1, 3));
console.log(findMean(arr, 0, 4));
Output
2 3 3
Complexity Analysis:
- 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).
// Javascript program to find floor value
// of mean in range l to r
let MAX = 1000005;
let prefixSum = new Array(MAX);
prefixSum.fill(0);
// To calculate prefixSum of array
function 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 r
function 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 code
let arr = [1, 2, 3, 4, 5];
let n = arr.length;
calculatePrefixSum(arr, n);
console.log(findMean(1, 2));
console.log(findMean(1, 3));
console.log(findMean(1, 4));
Output
2 3 3
Complexity Analysis:
- 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!
