[Java] Arithmetic Progressions

/* Use the slash-star style comments or the system won't see your
   identification information */
/*
ID: lincans1
LANG: JAVA
TASK: ariprog
*/
import java.io.*;
import java.util.*;

public class ariprog {
    
    
	private int MAX;

	private boolean DFS(int a, int b, int N, boolean[] flag) {
    
    
		if (N == 0) {
    
    
			return true;
		}
		if (a + b * N > MAX) {
    
    
			return false;
		}
		if (flag[a + b]) {
    
    
			return DFS(a + b, b, N - 1, flag);
		}
		else {
    
    
			return false;
		}
	}

	public ariprog() throws IOException {
    
    
		// Use BufferedReader rather than RandomAccessFile; it's much faster
		BufferedReader f = new BufferedReader(new FileReader("ariprog.in"));
		PrintWriter out = new PrintWriter(new BufferedWriter(new FileWriter("ariprog.out")));
		
		int N = Integer.parseInt(f.readLine());
		int M = Integer.parseInt(f.readLine());
		this.MAX = 2 * M * M;

		// find all the p^2 + q^2
		boolean[] flag = new boolean[MAX + 1];
		for (int p = 0; p <= M; p++) {
    
    
			for (int q = 0; q <= M; q++) {
    
    
				flag[p * p + q * q] = true;
			}
		}
		// push all elements to the list
		List<Integer> list = new ArrayList<>();
		for (int i = 0; i <= MAX; i++) {
    
    
			if (flag[i]) {
    
    
				list.add(i);
			}
		}
		// check every (a, b)
		boolean noSolution = true;
		for (int b = 1, n = MAX / (N - 1); b <= n; b++) {
    
    
			for (int a : list) {
    
    
				if (DFS(a, b, N- 1, flag)) {
    
    
					noSolution = false;
					out.println(a + " " + b);
				}
			}
		}
		if (noSolution) {
    
    
			out.println("NONE");
		}
		out.close();
		f.close();
	}
	
	public static void main (String [] args) throws IOException {
    
    
		new ariprog();
	}
}