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Largest Positive Integer That Exists With Its Negative

Difficulty: Easy

Problem Description

Given an integer array nums that does not contain any zeros, find the largest positive integer k such that -k also exists in the array. Return the positive integer k. If there is no such integer, return -1.

Key Insights

  • The problem requires finding a positive integer whose negative counterpart exists in the array.
  • A set can be used to efficiently check for the existence of negative values.
  • The algorithm should prioritize finding the largest positive integer.

Space and Time Complexity

Time Complexity: O(n)
Space Complexity: O(n)

Solution

To solve the problem, we can utilize a hash set to store all the integers from the array. Then, we will iterate through the array to check for each positive integer if its negative counterpart exists in the set. We track the largest valid positive integer found during this process. If no valid integer is found, we return -1.

  1. Create a set to store all integers from the nums array.
  2. Initialize a variable to keep track of the largest positive integer found.
  3. Iterate through the nums array:
    • If the current number is positive and its negative counterpart is in the set, update the largest positive integer if the current number is greater than the previously found largest.
  4. Return the largest positive integer found, or -1 if none exists.

Code Solutions

def findLargestK(nums):
    num_set = set(nums)  # Create a set for O(1) lookups
    largest_k = -1  # Initialize the largest positive integer
    
    for num in nums:
        if num > 0 and -num in num_set:  # Check if the positive number's negative exists
            largest_k = max(largest_k, num)  # Update largest_k if needed
            
    return largest_k  # Return the largest found or -1 if none found
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