Find the two that add up
A reconciliation tool looks for the two entries that together explain a difference.
- Return the two positions, counting from zero, smaller position first.
- If several pairs would work, return the one whose second position comes first.
- No pair means an empty list.
- A value may not be paired with itself, but two equal values at different positions are fine.
pairSummingTo(values: list<int>, target: 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 pairSummingTo(values []int, target int) []int {
}Worked examples
| Call | Result |
|---|---|
pairSummingTo([]int{2, 7, 11, 15}, 9) | []int{0, 1} |
pairSummingTo([]int{3, 2, 4}, 6) | []int{1, 2} |
pairSummingTo([]int{3, 3}, 6) | []int{0, 1} |
pairSummingTo([]int{1, 2}, 99) | []int{} |
Hint
Walk once, and for each value ask whether the number that would complete it has already gone by.
Reference solution in Go
func pairSummingTo(values []int, target int) []int {
seen := map[int]int{}
for j, v := range values {
need := target - v
if i, ok := seen[need]; ok {
return []int{i, j}
}
if _, ok := seen[v]; !ok {
seen[v] = j
}
}
return []int{}
}