Two Sum

Problem

Return indices of two numbers summing to a target; explain the container you'd use (e.g. in C++).

Example

[2,7,11,15], 9 -> [0,1]

Constraints

• 2 ≤ n ≤ 10^4

Note

Expect follow-ups on C++/STL knowledge. Use unordered_map and justify it.