Repeating array number (golang)

Hash table

package main

import "fmt"

func main() {
    a := [...]int{2,3,1,0,2,5,3}
    num := make(map[int]bool)
    for _, v := range a {
        if !num[v] {
            num[v] = true
        } else {
            fmt.Println(v)
        }
    }
}

Sort Find

package main

import (
    "fmt"
    "sort"
)

func main() {
    a := []int{2,3,1,0,2,5,3}
    sort.Ints(a)
    for i, v := range a {
        if i != v {
            if v == a[v] {
                fmt.Println(v)
            } else {
                a[i], a[v] = a[v], a[i]
            }
        }
    }
}