import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.io.StreamTokenizer;

public class Solving {

    public StreamTokenizer in  = new StreamTokenizer(new BufferedReader(new InputStreamReader(System.in)));
    public PrintWriter out  = new PrintWriter(new OutputStreamWriter(System.out));

    public static void main(String[] args) throws IOException {
        new Solving().run();
    }

    public int nextInt() throws IOException {
        in.nextToken();
        return (int) in.nval;
    }

    public void run() throws IOException {
        int num = this.nextInt();
        int[] arr = new int[num];
        int a = 0;
        int b = 0;
        for (int iter1 = 0; iter1 < num; iter1++) {
            arr[iter1] = this.nextInt() + this.nextInt();
        }
        StringBuilder str = new StringBuilder();
        for (int iter2 = (arr.length - 1); iter2 > 0; iter2--) {
            a = arr[iter2]/10 + arr[iter2 - 1]%10;
            str.insert(0, (a%10 + b));
            b = a/10;
        }
        if (b != 0) {
            str.insert(0, b);
        }
        str.append(arr[arr.length - 1]%10);
        this.out(str.toString());
    }

    public void out(String str) {
        out.println(str);
        out.flush();
    }
}

I don't know how make this faster. Help me please.

Edited by author 16.02.2014 03:25

How do you think what is the complexity of StringBuilder.insert() method?