Replay a log that can take it back
A stock adjustment screen records every change, and an undo command that cancels whichever change came last.
- A command is either a signed whole number to apply, or the word "undo".
- An undo cancels the most recent change that is still standing.
- An undo with nothing left to cancel does nothing.
- Start from zero and return the total once every command has run.
replayLog(commands: list<string>) → 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 replayLog(commands []string) int {
}Worked examples
| Call | Result |
|---|---|
replayLog([]string{"5", "3", "undo"}) | 5 |
replayLog([]string{"5", "undo", "undo"}) | 0 |
replayLog([]string{"10", "-4", "2"}) | 8 |
replayLog([]string{}) | 0 |
Hint
Keep the applied changes on a stack. Undo pops the last one off and subtracts it back out.
Reference solution in Go
func replayLog(commands []string) int {
applied := []int{}
total := 0
for _, command := range commands {
if command == "undo" {
if len(applied) > 0 {
total -= applied[len(applied)-1]
applied = applied[:len(applied)-1]
}
} else {
amount, _ := strconv.Atoi(command)
applied = append(applied, amount)
total += amount
}
}
return total
}