solve.swift

import Foundation
import Glibc

/*

Find the first unique number (value, not index) heading firstly
If there isn't return -1

value, count set.
order by value asc
return the value has 1 count
if not, return -1

*/

public func solution(_ A : inout [Int]) -> Int {
    // the value : (count, appearedAt)
    var countArr:[Int:(Int,Int)] = [:]

    for i in 0...A.count-1 {
        let val = A[i]

        if countArr[val] != nil {
            countArr[val]! = (countArr[val]!.0 + 1, countArr[val]!.1)
        }else{
            countArr[val] = (1,i)
        }
        
    }

    countArr = countArr.filter{ item in
        return item.value.0 == 1
    }

    let sorted = countArr.sorted(by: {
        $0.value.1 < $1.value.1
    })

    if(sorted.count == 0){
        return -1
    }

    return sorted[0].key
}