Rotate a list
A carousel shows the same items starting from a different one each time it advances.
- Rotating left by one moves the first item to the end.
- A shift larger than the list wraps around; a negative shift rotates the other way.
- An empty list rotates to an empty list.
rotateLeft(values: list<int>, by: int) → list<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 rotateLeft(values []int, by int) []int {
}Worked examples
| Call | Result |
|---|---|
rotateLeft([]int{1, 2, 3, 4}, 1) | []int{2, 3, 4, 1} |
rotateLeft([]int{1, 2, 3, 4}, 5) | []int{2, 3, 4, 1} |
rotateLeft([]int{1, 2, 3, 4}, -1) | []int{4, 1, 2, 3} |
rotateLeft([]int{1, 2, 3}, 0) | []int{1, 2, 3} |
Hint
Reduce the shift with a modulo first, and remember that the modulo of a negative number is negative in most of these languages.
Reference solution in Go
func rotateLeft(values []int, by int) []int {
n := len(values)
result := []int{}
if n == 0 {
return result
}
k := ((by % n) + n) % n
for i := 0; i < n; i++ {
result = append(result, values[(i+k)%n])
}
return result
}