How do you solve Find Lucky Integer in an Array on LeetCode?

Find Lucky Integer in an Array (LeetCode #1394) 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: Using a frequency map allows for efficient counting of occurrences.

What is the brute force solution for Find Lucky Integer in an Array?

The brute force approach for Find Lucky Integer in an Array is Brute Force, with O(n²) time complexity and O(1) space complexity. The brute force approach checks each number in the array and counts its occurrences to see if it matches its value. This is straightforward but inefficient, especially for larger arrays. The optimal Optimal Solution approach improves this to O(n).

What algorithm or data structure is used to solve Find Lucky Integer in an Array?

Find Lucky Integer in an Array uses the following concepts: Array, Hash Table, Counting. The recommended patterns to study are: Hash Map, Array.

What are the interview tips for Find Lucky Integer in an Array?

Always clarify the problem statement and constraints before jumping into coding. Discuss your thought process and approach with the interviewer to showcase your understanding. Test your solution with different edge cases to ensure robustness.

What are common mistakes when solving Find Lucky Integer in an Array?

Not considering edge cases where no lucky integer exists. Forgetting to convert the key to the correct type when comparing in languages like JavaScript.

#1394

Find Lucky Integer in an Array

Easy

ArrayHash TableCountingHash 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 solution uses a hash map to count the occurrences of each number in one pass, making it more efficient. This allows us to check for lucky integers in a single traversal.

⚙️

Algorithm

2 steps

1Step 1: Create a frequency map to count occurrences of each number in the array.
2Step 2: Iterate through the frequency map to find the largest lucky integer where the key equals its value.

solution.py8 lines

1def findLucky(arr):
2    from collections import Counter
3    freq = Counter(arr)
4    max_lucky = -1
5    for num, count in freq.items():
6        if num == count:
7            max_lucky = max(max_lucky, num)
8    return max_lucky

ℹ

Complexity note: The time complexity is O(n) because we traverse the array once to build the frequency map and then iterate through the map, which is much faster than the brute force approach. The space complexity is O(n) due to the storage of the frequency map.

1Using a frequency map allows for efficient counting of occurrences.
2The largest lucky integer is found by comparing keys and their values in the frequency map.

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