# Questions

```
Example 1:
Input: nums = [2,7,11,15], target = 9
Output: [0,1]
Output: Because nums[0] + nums[1] == 9, we return [0, 1].
Example 2:
Input: nums = [3,2,4], target = 6
Output: [1,2]
Example 3:
Input: nums = [3,3], target = 6
Output: [0,1]
```

**Implementation: TwoSum**

Assuming there are no duplicate numbers, we can keep a map of `number->index`

. The if the complement exists at a different index, we have found our pair.

### Time complexity

`O(n)`

### Space complexity

`O(n)`

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