2018/12/06 L1-030 一帮一 Java

import java.io.BufferedReader;
import java.io.InputStreamReader;

public class Main {

    public static void main(String[] args) throws Exception{
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        int num = Integer.parseInt(br.readLine());
        int oneNum = 0;
        int zeroNum = 0;
        String[][] str = new String[num][2];
        if (num >= 2 && num <= 50) {
            for(int i=0; i<num; i++) {
                str[i] = br.readLine().split(" ");
                if( Integer.parseInt(str[i][0]) == 1) {
                    oneNum++;
                } else if(Integer.parseInt(str[i][0]) == 0) {
                    zeroNum++;
                } else {
                    return;
                }
            }
            if (oneNum == zeroNum) {
                for(int i=0; i<num; i++) {
                    for(int j=num-1; j>0; j--) {
                        if(!str[i][0].equals(str[j][0]) && !str[i][0].equals("-1") && !str[j][0].equals("-1")) {
                            System.out.println(str[i][1] + " " + str[j][1]);
                            str[i][0] = "-1";
                            str[j][0] = "-1";
                            break;
                        }
                    }
                }
            } else {
                return;
            }
            
        } else {
            return;
        }

    }

}