Two Sum

Find two indices whose values add up to the target. Instead of checking every pair, remember what you've already seen.

nums = [3, 8, 2, 11, 7, 15] · target = 9Step 1 of 6

Start with an empty hash map. It will remember every number we've passed and where we saw it.

Kotlintime O(n) · space O(n)

1fun twoSum(nums: IntArray, target: Int): IntArray {

2 val seen = HashMap<Int, Int>()

3 for (i in nums.indices) {

4 val need = target - nums[i]

5 if (need in seen) return intArrayOf(seen[need]!!, i)

6 seen[nums[i]] = i

7 }

8 return intArrayOf()

Variables

i—

nums[i]—

need—

seen (hash map)value → index

empty

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