How many stretches add up to the figure
An investigator looks through a list of movements for every unbroken stretch that comes to a particular amount.
- Only consecutive movements count as a stretch.
- Stretches may overlap, and every one of them counts separately.
- Movements can be negative, so a longer stretch is not always a bigger total.
- Return how many stretches come to exactly the target.
stretchesTotalling(movements: list<int>, target: int) → int
Java 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
int stretchesTotalling(List<Integer> movements, int target) {
}Worked examples
| Call | Result |
|---|---|
stretchesTotalling(Main.<Integer>ls(1, 1, 1), 2) | 2 |
stretchesTotalling(Main.<Integer>ls(1, 2, 3), 3) | 2 |
stretchesTotalling(Main.<Integer>ls(1, -1, 0), 0) | 3 |
stretchesTotalling(Main.<Integer>ls(), 0) | 0 |
Hint
If the running total at two points differs by the target, the stretch between them is a hit. Keep a count of every running total you have seen and look up total minus target.
Reference solution in Java
int stretchesTotalling(List<Integer> movements, int target) {
Map<Integer, Integer> seen = new HashMap<>();
seen.put(0, 1);
int running = 0, hits = 0;
for (int movement : movements) {
running += movement;
hits += seen.getOrDefault(running - target, 0);
seen.merge(running, 1, Integer::sum);
}
return hits;
}