Solution: First Non-Repeating Integer in a List—Hashing

Let’s solve the First Non-Repeating Integer in a List—Hashing problem.

Statement

Given a list of integers, nums, find the first non-repeating integer in the list.

Constraints:

  • 11 \leq nums.length 103\leq 10^3

  • 5000-5000 \leq nums[i] 5000\leq 5000

Solution 1: Using a dictionary to keep count of repetitions

We track the frequency of each element in the list using a dictionary, which stores key-value pairs. The keys represent the elements of the list, and the values indicate how many times each element occurs.

  1. Initialize an empty dictionary, counts, to store the counts of each element.

  2. Iterate through the list of elements.

    1. If the element is already a key in counts, increment its value by 11 to represent its count.

    2. If the element is not in counts, add it to the dictionary with a count of 11.

  3. Iterate through the list again.

    1. Check the count of each element in counts.

    2. Return the first element with a count of 11.

Let’s look at the illustration below to better understand the solution:

Level up your interview prep. Join Educative to access 80+ hands-on prep courses.