How do you solve Degree of an Array on LeetCode?

Degree of an Array (LeetCode #697) can be solved using Brute Force or Optimal Solution. The optimal approach is Optimal Solution with O(n) time complexity and O(n) space complexity. Key insight: The degree of an array is determined by the maximum frequency of its elements.

What is the brute force solution for Degree of an Array?

The brute force approach for Degree of an Array is Brute Force, with O(n²) time complexity and O(1) space complexity. The brute force approach involves checking every possible subarray to find the degree and its minimum length. This is straightforward but inefficient because it examines all combinations. The optimal Optimal Solution approach improves this to O(n).

What algorithm or data structure is used to solve Degree of an Array?

Degree of an Array uses the following concepts: Array, Hash Table. The recommended patterns to study are: Hash Map, Array.

What are the interview tips for Degree of an Array?

Clarify the definition of the degree and subarray before starting. Discuss potential edge cases, such as arrays with all unique elements. Explain your thought process clearly while coding.

What are common mistakes when solving Degree of an Array?

Not considering all elements that contribute to the degree. Overlooking the need to track first and last occurrences.

#697

Degree of an Array

Easy

ArrayHash TableHash MapArray

LeetCode ↗

Approaches

Brute ForceOptimal

Complexity Comparison

	Brute Force	Optimal Solution★
Time	O(n²)	O(n)
Space	O(1)	O(n)

💡

Intuition

Time O(n)Space O(n)

The optimal approach uses a single pass to count frequencies and track the first and last positions of each element. This allows us to efficiently determine the minimum length of the subarray with the same degree.

⚙️

Algorithm

3 steps

1Step 1: Count the frequency of each element and track their first and last occurrence indices.
2Step 2: Determine the degree of the array from the frequency count.
3Step 3: For each element that contributes to the degree, calculate the length of the subarray from its first to last occurrence and update the minimum length.

solution.py18 lines

1# Full working Python code
2from collections import defaultdict
3
4def findShortestSubarray(nums):
5    count = defaultdict(int)
6    first = {}
7    last = {}
8    for i, num in enumerate(nums):
9        count[num] += 1
10        if num not in first:
11            first[num] = i
12        last[num] = i
13    degree = max(count.values())
14    min_length = float('inf')
15    for num in count:
16        if count[num] == degree:
17            min_length = min(min_length, last[num] - first[num] + 1)
18    return min_length

ℹ

Complexity note: This complexity is linear because we traverse the array a constant number of times, resulting in a single pass for counting and another for determining the minimum length.

1The degree of an array is determined by the maximum frequency of its elements.
2To find the smallest subarray with the same degree, track first and last occurrences of elements.

Solutions and explanations are original Tejav content. Problem titles © LeetCode — use the LeetCode button above for the full problem statement.