How do you solve Maximum Number of Pairs in Array on LeetCode?

Maximum Number of Pairs in Array (LeetCode #2341) 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: Counting frequencies helps in determining pairs efficiently.

What is the brute force solution for Maximum Number of Pairs in Array?

The brute force approach for Maximum Number of Pairs in Array is Brute Force, with O(n²) time complexity and O(1) space complexity. The brute force approach involves checking every possible pair of integers in the array to see if they are equal. If they are, we remove them and count how many pairs we can form. This method is straightforward but inefficient. The optimal Optimal Solution approach improves this to O(n).

What algorithm or data structure is used to solve Maximum Number of Pairs in Array?

Maximum Number of Pairs in Array uses the following concepts: Array, Hash Table, Counting. The recommended patterns to study are: Hash Map, Array.

What are the interview tips for Maximum Number of Pairs in Array?

Always think about counting problems in terms of frequency. Consider edge cases, such as all unique numbers or all identical numbers. Discuss your thought process out loud to show your understanding of the problem.

What are common mistakes when solving Maximum Number of Pairs in Array?

Not considering the frequency of numbers, leading to incorrect pairs. Using nested loops without realizing a counting method is more efficient.

#2341

Maximum Number of Pairs in 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 frequency count to determine how many pairs can be formed. By counting how many times each number appears, we can easily calculate the number of pairs and leftovers without needing to check each pair explicitly.

⚙️

Algorithm

5 steps

1Step 1: Create a frequency array to count occurrences of each number in nums.
2Step 2: Iterate through the frequency array to calculate pairs and leftovers.
3Step 3: For each number, the number of pairs is frequency divided by 2, and leftovers are frequency modulo 2.
4Step 4: Sum the pairs and calculate the total leftovers.
5Step 5: Return the total pairs and leftovers.

solution.py12 lines

1# Full working Python code
2
3def maxPairs(nums):
4    freq = [0] * 101
5    for num in nums:
6        freq[num] += 1
7    pairs = 0
8    leftovers = 0
9    for count in freq:
10        pairs += count // 2
11        leftovers += count % 2
12    return [pairs, leftovers]

ℹ

Complexity note: The time complexity is O(n) because we only iterate through the array a couple of times. The space complexity is O(n) due to the frequency array, which is fixed at size 101.

1Counting frequencies helps in determining pairs efficiently.
2Pairs can be formed from even counts, and leftovers from odd counts.

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