Question

I’m doing Project Euler #22:

Using names.txt (right click and ‘Save Link/Target As…’), a 46K text
file containing over five-thousand first names, begin by sorting it
into alphabetical order. Then working out the alphabetical value for
each name, multiply this value by its alphabetical position in the
list to obtain a name score.

For example, when the list is sorted into alphabetical order, COLIN,
which is worth 3 + 15 + 12 + 9 + 14 = 53, is the 938th name in the
list. So, COLIN would obtain a score of 938 × 53 = 49714.

What is the total of all the name scores in the file?

Compiling my code below with Cygwin’s gcc-g++ compiler, the answer is 871129635. But with Visual Studio 2008, the answer is correct, 871198282. Why is this the case?

#include<iostream>
#include<fstream>
#include<vector>
#include<algorithm>
using namespace std;

bool strCmp(string x, string y) {
    if(x.compare(y) == -1)
        return true;
    else
        return false;
}

int getScore(string s) {
    int score = 0;
    for(unsigned int i = 0; i < s.length(); i++)
        score += (((int) s.at(i)) - 64);
    return score;
}

int getTotalScore(vector<string> names) {
    int total = 0;
    for(unsigned int i = 0; i < names.size(); i++)
        total += (getScore(names[i]) * (i+1));
    return total;
}

int main() {
    vector<string> names;
    ifstream namesFile("names.txt");

    char curChar;
    string curName = "";

    //get names from file
    if(namesFile.is_open()) {
        while(!namesFile.eof()) {
            curChar = namesFile.get();

            if(isalpha(curChar))
                curName.push_back(curChar);
            else {
                if(!curName.empty()) {//store finished name
                    names.push_back(curName);
                    curName.clear();
                }
            }
        }
    }
    namesFile.close();

    //alphabetize
    sort(names.begin(), names.end(), strCmp);

    //count up name scores
    cout << getTotalScore(names) << endl;
    return 0;
}

Answer 1

Here:

if(x.compare(y) == -1)

You are assuming that std::string::compare will return -1 for a less-than result, but it can in fact return any negative value. You can fix this by using x.compare(y) < 0, but it’s better to just write x<y. In fact, you don’t even need the strCmp function because the default behavior of std::sort is to compare the elements using operator<.