f = open("/path/to/file");
    // do something with file

vs.

    d = opendir("path/to")
    while((dent = readdir(d)) != NULL) {
       if(!dent.name.startsWith("file"))
          continue;
       // do something with first matched entry
    }

The former is O(log n) on ext4, O(n) on older filesystems that use flat lists.

The latter is always O(n)