RepeatedNTimesIII.swift

Check if A[i] == A[i - 1] or A[i] == A[i - 2]
If so, we return A[i]
If not, it must be [x, x, y, z] or [x, y, z, x].
We return A[0] for the cases that we miss.
O(N) time O(1) space

class Solution {
    func repeatedNTimesIII(_ A: [Int]) -> Int {
     
    for i in 2..<A.count {
        if A[i] == A[i-1] || A[i] == A[i-2] {
            return A[i]
        }
    }
    
    return A[0]
    }
}