Problem Statement

A company currently pays a fixed sum for the use of a particular licensed software package.   In determining if it has a good deal it decides to calculate its maximum use of the software from its license management log file. Assume the software's licensing daemon faithfully records a checkout event when a copy of the software starts and a checkin event when the software finishes to its log file. An example of checkout and checkin events are:

Save the 10,000 line log file from   here   into a local file, then write a program to scan the file extracting both the maximum licenses that were out at any time, and the time(s) at which this occurs. Mirror of log file available as a zip here (offsite mirror).

Let's start with the solution:

void main() {
    import std.stdio;
    int nOut, maxOut = -1;
    string[] maxTimes;

    foreach (string job; lines(File("mlijobs.txt"))) {
        nOut += (job[8] == 'O') ? 1 : -1;
        if (nOut > maxOut) {
            maxOut = nOut;
            maxTimes = null;
        }
        if (nOut == maxOut)
            maxTimes ~= job[14 .. 33];
    }

    writefln("Maximum simultaneous license use is %d at" ~
             " the following times:\n%( %s\n%)", maxOut, maxTimes);
}