Ruudukko

import java.util.Arrays;
 
 
public class Main {
 
	public static void main(String[] args) {
		
		IO io = new IO();
 
		int n = io.nextInt();
		
		String[] characters = new String[n * n];
		
		for (int i = 0; i < n; i++) {
			char[] row = io.next().toCharArray();
			for (int j = 0; j < n; j++) {
				int index = j + i * n;
				characters[index] = row[j]+"";
			}
		}
		
		int xi = 0, yi = 0;
		
		for (int i = 1; i < 2 * n - 1; i++) {
			for (int x = 0; x <= i; x++) {
				int index = x + (i - x) * n;
				if(x >= n || i - x >= n 
						 || x < xi || i - x < yi) continue;
				String up = null, left = null;
				
				if(x != 0) {
					left = characters[index-1];
				}
				if((i - x) != 0) {
					up = characters[index-n];
				}
				String better = better(up, left);
				if(up != left && up != null && left != null) {
					if(up.equals(better)) {
						xi = x;
					} else {
						yi = i - x;
					}
				}
				characters[index] = better.concat(characters[index]);
			}
		}
		
		io.println(characters[n*n-1]);
		
		io.close();
		
	}
	
	public static String better(String up, String left) {
		if(up == null) return left;
		if(left == null) return up;
		if(up.length() > left.length()) return up;
		if(left.length() > up.length()) return left;
		for (int i = 0; i < up.length(); i++) {
			if(up.charAt(i) < 
					left.charAt(i)) {
				return up;
			}
			if(up.charAt(i) > 
					left.charAt(i)) {
				return left;
			}
		}
			
		return up;
	}
 
}

Test 1

Group: 1

Verdict: ACCEPTED

Test 2

Group: 1

Verdict: ACCEPTED

Test 3

Group: 1

Verdict: ACCEPTED

Test 4

Group: 1

Verdict: ACCEPTED

Test 5

Group: 1

Verdict: ACCEPTED

Test 6

Group: 2

Verdict: ACCEPTED

Test 7

Group: 2

Verdict: WRONG ANSWER

Test 8

Group: 2

Verdict: WRONG ANSWER

Test 9

Group: 2

Verdict: WRONG ANSWER

Test 10

Group: 2

Verdict: WRONG ANSWER

Test 11

Group: 3

Verdict: ACCEPTED

Test 12

Group: 3

Verdict: WRONG ANSWER

Test 13

Group: 3

Verdict: WRONG ANSWER

Test 14

Group: 3

Verdict: WRONG ANSWER

Test 15

Group: 3

Verdict: WRONG ANSWER