[Amazon Question] Largest Unique Number in an array

Problem: Given an array of integers, return the largest integer that only occurs once. If no integer occurs once, return -1.

Example:

Input: [2,5,3,7,4,7,2,3]
Output: 5
Explanation: The maximum integer in the array is 7 but it is repeated. The number 5 occurs only once, so it's the answer.

Approach: We can solve it using hashing easily. Just look at the implementation to understand the approach.

Implementation in C#:

    public int LargestUniqueNumber(int[] nums) 

    {

        Dictionary<int, int> freqMap = new Dictionary<int, int>();

        foreach(int num in nums)

        {

            if (!freqMap.ContainsKey(num))

            {

                freqMap[num] = 0;

            }

            ++freqMap[num];

        }

        int max = int.MinValue;

        foreach(var kv in freqMap)

        {

            if (kv.Value == 1 && kv.Key > max)

            {

                max = kv.Key;

            }

        }        

        return max == int.MinValue ? -1 : max;

    }

Complexity: O(n)