The first repeat
A stream of ids is meant to be unique; the audit flags the first value that turns up twice.
- Scan left to right and stop at the first value that has appeared earlier.
- A value repeated later does not matter if a smaller repeat came first.
- No value repeats at all gives -1.
firstRepeating(values: list<int>) → int
Go needs a compiler and Drill does not host one yet, so this page is the reference rather than an exercise: the problem, worked examples, and the solution in full. To type it out, the same problem runs in Python.
Where you start
func firstRepeating(values []int) int {
}Worked examples
| Call | Result |
|---|---|
firstRepeating([]int{2, 1, 3, 1}) | 1 |
firstRepeating([]int{1, 2, 3}) | -1 |
firstRepeating([]int{4, 4}) | 4 |
firstRepeating([]int{7, 7, 7}) | 7 |
Hint
A set of everything so far; the moment you add one that is already there, that is the answer.
Reference solution in Go
func firstRepeating(values []int) int {
seen := map[int]bool{}
for _, v := range values {
if seen[v] {
return v
}
seen[v] = true
}
return -1
}