Challenge #249 [Easy] Playing the Stock Market

/*
[2016-01-11] Challenge #249 [Easy] Playing the Stock Market

https://www.reddit.com/r/dailyprogrammer/comments/40h9pd/20160111_challenge_249_easy_playing_the_stock/?sort=top
*/
#include <iostream>
#include <fstream>
#include <vector>
#include <string>


//Read in the inputFile and return the vector
std::vector<double> readFile(std::string fileName) {
    std::vector<double> vec;

    std::ifstream inputFile(fileName);

    if (inputFile.is_open()) {
        double val;
        // Read from file until empty
        while (inputFile >> val) {
            vec.push_back(val); // Store in vector only valid values.
        }
    }

    inputFile.close(); // not really needed, would be automagically closed when out of scope.

    return vec;
}


int main() {

    std::vector<double> vec = readFile("inputFile.txt");

    if (vec.size() <= 2) {
        std::cout << "Error: unable to load data from inputFile.txt" << std::endl;
        return 1;
    }

    double bestProfit = 0;
    double buy = 0;
    double sell = 0;
    constexpr long delay = 1; // 0 = test next, 1 = test with one tick delay

    // Slow but tests all cases.
    auto last = std::prev(vec.end(), delay); // adjust end point for the look ahead start point
    for (auto buyLoop = vec.begin(); buyLoop != last; ++buyLoop) {

        auto sellLoop = std::next(buyLoop, delay); // adjust starting look-ahead for tick delay
        for (++sellLoop; sellLoop != vec.end(); ++sellLoop) {

            // Check if this buy/sell combo is better then the current best
            double profit = *sellLoop - *buyLoop;
            if (profit > bestProfit) {
                bestProfit = profit;
                buy = *buyLoop;
                sell = *sellLoop;
            }
        }
    }
    std::cout << "buy sell profit : " << buy << " " << sell << " " << bestProfit << std::endl;

    return 0;
}