Here's a solution in Go. package main import ( "fmt" ) func main() { // a is the sample array a := []int{0,2, 3, 3}

Here's a solution in Go. package main import ( "fmt" ) func main() { // a is the sample array a := []int{0,2, 3, 3} // Reorder values such that a[i] == i when i is not the missing value. for i := 0; i < len(a); i++ { j := a[i] k := a[j] a[j] = j a[i] = k } // Look for a[i] != i for i := 0; i < len(a); i++ { if a[i] != i { fmt.Println("missing:", i, "duplicate:", a[i]) break } } } This is a simple expression of a solution. The code can be improved.