Question

In an online judge programming contest problem I am required to output up to 50,000 lines in under 1 second via standard out (in addition to reading in up to 200,000 pairs of integers which I used a buffer for). My logic seems to be correct but I keep getting my submissions turned down for exceeding the 1 second runtime. I stripped down my code logic to just output a constant string and it still exceeds the time limit.

Is there a faster way to output than using System.out.println(String s)for every line of output?

Answer 1

I would use a single System.out.print call (or the least that makes sense which is to be found out via benchmarking) like this:

String str = "line1\nline2\nline3\n ...";
System.out.print(str);

Edit:

    StringBuilder sb = new StringBuilder();
    for (int i = 0; i < 500000; i++) {
        sb.append(i).append("\n");
    }
    String str = sb.toString();
    long nt = System.nanoTime();
    System.out.print(str);
    nt = System.nanoTime() - nt;
    System.out.print("\nTime(ms): " + (double)nt / 1000000);

sb.toString() is not a free operation.

The above takes ~650ms on my notebook (500,000 instead of the requested 50,000).

Edit2: with two other tricks, in case the filling time matters:

• construct the StringBuilder with a sufficient capacity

• don’t append
  for every line (the code below appends 200 lines every time, for this
  it uses a temp sb1); only possible if every line can have the same
  content. Enjoy.

  long nt = System.nanoTime();
  StringBuilder sb1 = new StringBuilder(400);
  for (int i = 0; i < 200; i++) {
      sb1.append("l").append("\n");
  }
  String strSb1 = sb1.toString();
  
  StringBuilder sb = new StringBuilder(1000000);
  for (int i = 0; i < 2500; i++) {
      sb.append(strSb1);
  }
  
  System.out.print(sb.toString());
  nt = System.nanoTime() - nt;
  System.out.print("\nTime(ms): " + (double)nt / 1000000);
  

~500ms in my case.