gistfile1.cpp

#include <array>
#include <iostream>
#include <unordered_map>

int main() {
  auto numbers = std::array<int, 4>{2, 7, 11, 15};
  auto table = std::unordered_map<int, int>();
  int target = 9;
  for (int i = 0; i < numbers.size(); ++i) {
    auto m = table.find(target - numbers[i]);
    if (m != table.end()) {
      std::cout <<"index1=" << m->second + 1 << ", index2=" << i + 1 << std::endl;
      break;
    }
    table[numbers[i]] = i;
  }
  return 0;
}