Ruudukko

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;


public class Ruudukkokulkija {

	static int n;
	static char[][] r;
	
	public static void main(String[] args) {
		IO io = new IO();
		
		n = io.nextInt();
		
		r = new char[n][];
		
		for (int i = 0; i < n; i++) {
			r[i] = io.next().toCharArray();
		}
		
		io.println(mene("", new ArrayList<Pair>(Arrays.asList(new Pair(0, 0)))));
		
		io.close();
	}

	static class Pair {
		int x;
		int y;
		Pair(int x, int y) {
			this.x = x; this.y = y;
		}
	}
	
	static String mene(String a, List<Pair> coordinates) {
		
		while (true) {
		
			char min = 'Z';
			
			for (int i = 0; i < coordinates.size(); i++) {
				int x = coordinates.get(i).x;
				int y = coordinates.get(i).y;
				if (r[y][x] < min) min = r[y][x];
				else if (r[y][x] > min) {
					coordinates.remove(i--);
				}
			}
			a = a + min;
			int len = coordinates.size();
			for (int i = 0; i < len; i++) {
				Pair c = coordinates.get(i);
				int x = c.x;
				int y = c.y;
				if (r[y][x] > min) {
					coordinates.remove(i--);
					len--;
				} else lbl: {
					if (x+1 == n && y+1 == n) {
						return a;
					}
					
					if (x+1 == n) {
						c.y++;
						break lbl;
					}
					
					if (y+1 == n) {
						c.x++;
						break lbl;
					}
					
					char asz = r[y+1][x];
					char bsz = r[y][x+1];
					if (asz < bsz) c.y++; else
					if (bsz < asz) c.x++; else
					{
						coordinates.add(new Pair(c.x+1, c.y));
						c.y++;
					}
				}
			}
		
		}
	}
	
}

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: TIME LIMIT EXCEEDED

Test 7

Group: 2

Verdict: TIME LIMIT EXCEEDED

Test 8

Group: 2

Verdict: ACCEPTED

Test 9

Group: 2

Verdict: ACCEPTED

Test 10

Group: 2

Verdict: ACCEPTED

Test 11

Group: 3

Verdict: TIME LIMIT EXCEEDED

Test 12

Group: 3

Verdict: TIME LIMIT EXCEEDED

Test 13

Group: 3

Verdict: ACCEPTED

Test 14

Group: 3

Verdict: ACCEPTED

Test 15

Group: 3

Verdict: TIME LIMIT EXCEEDED