题解 | #涂颜料#

import java.util.Scanner;



public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        int q = in.nextInt();
        char[] color = {'B', 'R', 'G'};
        int[] diff = new int[n + 1];
        while (q > 0) {
            int start = in.nextInt();
            int end = in.nextInt();
            diff[start] += 1;
		  	// 如果end在数组的结尾出，没必要将[end, -1]区间的元素减一
            if(end + 1 < n + 1) diff[end + 1] -= 1;
            q--;
        }

        for (int i = 1; i <= n; i++) {
            diff[i] = diff[i - 1] + diff[i];
        }
        for (int i = 1; i <= n ; i++) {
            if(diff[i] == 0){
                System.out.print('O');
            }else if(diff[i] % 3 == 0){
                System.out.print('B');
            }else if(diff[i] % 3 == 1){
                System.out.print('R');
            }else{
                System.out.print('G');
            }
        }
    }
}