Is Missing Number In Arithmetic Progression easy or hard?

LeetCode classifies this problem as Easy because it relies on basic arithmetic progression properties and a simple linear scan of the array. The challenge is recognizing how to compute the expected common difference and detect where the pattern breaks.

Missing Number In Arithmetic Progression Python/Java solution

Both Python and Java implementations follow the same idea: compute the common difference and iterate through the array until the difference between adjacent elements changes. At that point, return arr[i] + diff. The algorithm runs in O(n) time with constant extra space.

How to solve Missing Number In Arithmetic Progression in O(n)?

First compute the expected common difference using (arr[n-1] - arr[0]) / n. Then iterate through the array and compare arr[i+1] - arr[i] with the expected difference. When the difference is larger than expected, the missing number must be arr[i] + diff.

What is the best approach for Missing Number In Arithmetic Progression?

The most common approach is computing the expected common difference and scanning the array to find where the difference breaks. Once a pair of adjacent elements does not match the expected difference, the missing number is simply the previous value plus the difference. This solution runs in O(n) time and O(1) space.

Is Missing Number In Arithmetic Progression asked at Google/Amazon/Meta?

Arithmetic progression and missing-number problems appear frequently in interviews at companies like Amazon, Google, and Microsoft. They test your understanding of mathematical patterns, array traversal, and edge-case reasoning.

What data structure is used in Missing Number In Arithmetic Progression?

The problem primarily uses arrays and simple arithmetic operations. No advanced data structures are required since the progression property allows you to detect the missing value with a linear scan.

What is the time complexity of Missing Number In Arithmetic Progression?

The optimal solution runs in O(n) time because you only need a single pass through the array to detect where the arithmetic progression breaks. Both the traversal approach and the arithmetic sum approach also use O(1) extra space.

Description Hints 3 Solution Video 2:59

1228. Missing Number In Arithmetic Progression

Easy52.0% acceptance2 companiesPremium elsewhere, free here

In some array arr, the values were in arithmetic progression: the values arr[i + 1] - arr[i] are all equal for every 0 <= i < arr.length - 1.

A value from arr was removed that was not the first or last value in the array.

Given arr, return the removed value.

Example 1:

Input: arr = [5,7,11,13]
Output: 9
Explanation: The previous array was [5,7,9,11,13].

Example 2:

Input: arr = [15,13,12]
Output: 14
Explanation: The previous array was [15,14,13,12].

Constraints:

3 <= arr.length <= 1000
0 <= arr[i] <= 10⁵
The given array is guaranteed to be a valid array.

Asked at 2 companies

Audible Amazon

Topics

Array Math

Hints open one at a time

Hint 1

Assume the sequence is increasing, what if we find the largest consecutive difference?

Hint 2

Is the missing element in the middle of the segment with the largest consecutive difference?

Hint 3

For decreasing sequences, just reverse the array and do a similar process.

2:59

Still stuck?Read 2 approaches, or watch a walkthrough.

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1class Solution:
  def solve(self):
      pass


Starter codePython 3Spaces: 4

Examples

Case 1Case 2

Input

[5,7,11,13]

Input

[15,13,12]

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