Max Average Stock Price Solution Amazon OA 2022

Max Average Stock Price Solution

The interns at Amazon were asked to review the company’s stock value over a period. Given the stock prices of n months, the net price change for the ith month is defined as the absolute difference between the average of stock prices for the first i months and for the remaining (n – i) months where 1≤ i <n. Note that these averages are rounded down to an integer.

Given an array of stock prices, find the month at which the net price change is minimum. If there are several such months, return the earliest month.

Note: The average of a set of integers here is defined as the sum of integers divided by the number of integers, rounded down to the nearest integer. For example, the average of [1, 2, 3, 4] is the floor of (1 + 2 + 3 + 4) / 4 = 2.5 and the floor of 2.5 is 2.

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  • stockPrice = [1, 3, 2, 3]
  • The minimum net price change is 0, and it occurs in the 2nd month. Return 2.

Function Description

  • Complete the function findEarliestMonth the editor below.
  • findEarliestMonth has the following parameter: int stockPrice[n]: the stock prices


int: the earliest month in which the net price change is minimum


  • 2 ≤ n ≤ 105
  • 1 ≤ stockPrice[i] ≤ 109

Sample Input

STDIN               FUNCTION
------             ----------
5            ->    stockPrice[]
size n = 5
1            ->    stockPrice = [1, 3, 2, 4, 5]

Sample Output



The net price change can be calculated as:

  • Month 1: [1] and [3, 2, 4, 5], their respective averages, rounded down = 1 and 3, net price change = 2
  • Month 2: [1, 3] and [2, 4, 5], averages = 2 and 3, net price change = 1
  • Month 3: [1, 3, 2] and [4, 5], averages = 2 and 4, net price change = 2
  • Month 4: [1, 3, 2, 4] and [5], averages = 2 and 5, net price change = 3

The minimum net price change is 1, and it occurs at month 2.

Sample Input 1

STDIN               FUNCTION
------             ----------
6            ->    stockPrice[]
size n = 6
1            ->    stockPrice = [1, 1, 1, 1, 1, 1]

Sample Output 1



Since all the stock prices are all the same, the average is always 1 and the net price change is always 0. The earliest month this occurs is 1.

Max Average Stock Price Amazon OA
Max Average Stock Price Amazon OA


Code: Max Average Stock Price Solution

public int maxAverage(int[] prices) {
 int n = prices.length;
 int[] postfix = new int[n];
 int sum = 0;
 for(int i=n-1; i>=0; i--) {
  postfix[i] = sum;
 int ans = 0;
 sum = 0;
 for(int i=0; i<n; i++) {
  int preAverage = sum/(i-0+1);
  int postAverage = postfix[i]==0? postfix[i] : postfix[i]/(n-1-i);
  ans = Math.max(ans, Math.abs(preAverage-postAverage));
 return ans;

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