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Formatted question description: https://leetcode.ca/all/2256.html

2256. Minimum Average Difference

  • Difficulty: Medium.
  • Related Topics: Array, Prefix Sum.
  • Similar Questions: Split Array With Same Average, Number of Ways to Split Array.

Problem

You are given a 0-indexed integer array nums of length n.

The average difference of the index i is the absolute difference between the average of the first i + 1 elements of nums and the average of the last n - i - 1 elements. Both averages should be rounded down to the nearest integer.

Return** the index with the minimum average difference. If there are multiple such indices, return the **smallest one.

Note:

  • The absolute difference of two numbers is the absolute value of their difference.

  • The average of n elements is the sum of the n elements divided (integer division) by n.

  • The average of 0 elements is considered to be 0.

  Example 1:

Input: nums = [2,5,3,9,5,3]
Output: 3
Explanation:
- The average difference of index 0 is: |2 / 1 - (5 + 3 + 9 + 5 + 3) / 5| = |2 / 1 - 25 / 5| = |2 - 5| = 3.
- The average difference of index 1 is: |(2 + 5) / 2 - (3 + 9 + 5 + 3) / 4| = |7 / 2 - 20 / 4| = |3 - 5| = 2.
- The average difference of index 2 is: |(2 + 5 + 3) / 3 - (9 + 5 + 3) / 3| = |10 / 3 - 17 / 3| = |3 - 5| = 2.
- The average difference of index 3 is: |(2 + 5 + 3 + 9) / 4 - (5 + 3) / 2| = |19 / 4 - 8 / 2| = |4 - 4| = 0.
- The average difference of index 4 is: |(2 + 5 + 3 + 9 + 5) / 5 - 3 / 1| = |24 / 5 - 3 / 1| = |4 - 3| = 1.
- The average difference of index 5 is: |(2 + 5 + 3 + 9 + 5 + 3) / 6 - 0| = |27 / 6 - 0| = |4 - 0| = 4.
The average difference of index 3 is the minimum average difference so return 3.

Example 2:

Input: nums = [0]
Output: 0
Explanation:
The only index is 0 so return 0.
The average difference of index 0 is: |0 / 1 - 0| = |0 - 0| = 0.

  Constraints:

  • 1 <= nums.length <= 105

  • 0 <= nums[i] <= 105

Solution (Java, C++, Python)

  • class Solution {
    public int minimumAverageDifference(int[] nums) {
        long numsSum = 0;
        for (int num : nums) {
            numsSum += num;
        }
        long minAverageDiff = Long.MAX_VALUE;
        long sumFromFront = 0;
        int index = 0;
        for (int i = 0; i < nums.length; i++) {
            sumFromFront += nums[i];
            int numbersRight = i == nums.length - 1 ? 1 : nums.length - i - 1;
            long averageDiff =
                    Math.abs(sumFromFront / (i + 1) - (numsSum - sumFromFront) / numbersRight);
            if (minAverageDiff > averageDiff) {
                minAverageDiff = averageDiff;
                index = i;
            }
            if (averageDiff == 0) {
                break;
            }
        }
        return index;
    }
}

  • Todo

  • class Solution:
    def minimumAverageDifference(self, nums: List[int]) -> int:
        s = list(accumulate(nums))
        ans, n = 0, len(nums)
        mi = inf
        for i in range(n):
            a = s[i] // (i + 1)
            b = 0 if i == n - 1 else (s[-1] - s[i]) // (n - i - 1)
            t = abs(a - b)
            if mi > t:
                ans = i
                mi = t
        return ans

############

# 2256. Minimum Average Difference
# https://leetcode.com/problems/minimum-average-difference/

class Solution:
    def minimumAverageDifference(self, nums: List[int]) -> int:
        mmin = float('inf')
        res = -1
        n = len(nums)
        curr = 0
        s = sum(nums)
        
​
        for i, x in enumerate(nums):
            left = i + 1
            right = n - i - 1
            
            curr += x
            s -= x
​
            if i == n - 1:
                ans = abs(floor(curr / left))
            else:
                ans = abs(floor(curr / left) - floor(s / right))
            # print(i, ans)
            if ans < mmin:
                mmin = ans
                res = i
        
        return res

Explain:

nope.

Complexity:

  • Time complexity : O(n).
  • Space complexity : O(n).

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