Create two-sum.cpp

Note:
The sorted index != original index. 2 Options:
1. Search for the original index with the value;
2. Use a map with key == number and value == original Index (starts from 1), and for i = 1 ... target / 2 that has map[i] > 0, check if there is a j = target - i that has map[j] > 0. Return the satisfied i and j.