package main

import (
    "fmt"
)

func abs(x int) int {
    if x < 0 {
        return -x
    }
    return x
}

func max(x, y int) int {
    if x > y {
        return x
    }
    return y
}

func min(x, y int) int {
    if x < y {
        return x
    }
    return y
}

func repeatedNumber(A []int) []int {
    sum := 0
    shouldBeSum := (len(A) * (len(A) + 1)) / 2
    repeatingNumber := 0

    for i := range A {
        sum += abs(A[i])
        index := abs(A[i]) - 1
        if A[index] > 0 {
            A[index] = -A[index]
        } else {
            repeatingNumber = index + 1
        }
    }

    missingNumber := shouldBeSum - (sum - repeatingNumber)

    return []int{repeatingNumber, missingNumber}
}

func main() {
    fmt.Println(repeatedNumber([]int{3, 1, 2, 5, 3}))
}