Problems › JavaScript › patterns
The two readings that add up
A reconciliation tool has a sorted column of amounts and a difference to explain. It looks for the two amounts that together account for it.
- The amounts arrive sorted ascending.
- Return the two amounts, smaller first.
- If several pairs work, return the one with the smallest first amount.
- If no pair adds up, return an empty list.
- An amount cannot pair with itself — the two have to be at different positions.
pairSummingTo(amounts: list<int>, target: int) → list<int>
Where you start
function pairSummingTo(amounts, target) {
}Worked examples
| Call | Result |
|---|---|
pairSummingTo([1,2,4,7,11], 9) | [2,7] |
pairSummingTo([1,2,3,4], 5) | [1,4] |
pairSummingTo([1,2,3], 100) | [] |
pairSummingTo([], 3) | [] |
Hint
Sorted input means you can start at both ends. If the two ends add up to too much, the right end is too big; if too little, the left end is too small.
Reference solution in JavaScript
function pairSummingTo(amounts, target) {
let i = 0;
let j = amounts.length - 1;
while (i < j) {
const sum = amounts[i] + amounts[j];
if (sum === target) return [amounts[i], amounts[j]];
if (sum < target) i += 1;
else j -= 1;
}
return [];
}