Ruudukko

import java.io.BufferedOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;

public class Main {
    private static int n;
    private static int x = 0;
    private static int y = 0;
    public static void main(String[] args) {
        IO io = new IO();
        
        n = io.nextInt();
        
        char[][] arr = new char[n][n];
        
        for (int p = 0; p < n; p++) {
            String s = io.next();
            for (int o = 0; o < n; o++) {
                arr[p][o] = s.charAt(o);
            }
        }
        
        String str = "" + arr[0][0];
        
        while (x != n - 1 || y != n - 1) {
            int tempX = x;
            int tempY = y;
            char nxt = next(arr, tempX, tempY, true, 1);
            //System.out.println(x + " " + y);
            str += arr[y][x];
        }
        
        io.println(str);
        
        io.close();
    }
    
    private static char next (char[][] arr, int tx, int ty, boolean first, int iter) {
        if (tx == n - 1 && ty == n - 1) {
            return arr[ty][tx];
        } else if (tx == n - 1) {
            if (first) y++;
            ty++;
        } else if (ty == n - 1) {
            if (first) x++;
            tx++;
        } else {
            char cy = arr[ty + 1][tx];
            char cx = arr[ty][tx + 1];
            if (cy < cx) {
                if (first) y++;
                ty++;
            } else if (cx < cy) {
                if (first) x++;
                tx++;
            } else {
                int tempX = tx;
                int tempY = ty;
                char nx = next(arr, tempX + 1, tempY, false, iter + 1);
                char ny = next(arr, tempX, tempY + 1, false, iter + 1);
                if (ny < nx) {
                    if (first) y++;
                    ty++;
                } else if (nx < ny) {
                    if (first) x++;
                    tx++;
                } else {
                    if (first) x++;
                    tx++;
                }
            }
        }
        return arr[ty][tx];
    }
}

class IO extends PrintWriter {
	private InputStreamReader r;
	private static final int BUFSIZE = 1 << 15;
	private char[] buf;
	private int bufc;
	private int bufi;
	private StringBuilder sb;
	
	public IO() {
		super(new BufferedOutputStream(System.out));
		r = new InputStreamReader(System.in);
		
		buf = new char[BUFSIZE];
		bufc = 0;
		bufi = 0;
		sb = new StringBuilder();
	}
	
	private void fillBuf() throws IOException {
		bufi = 0;
		bufc = 0;
		while(bufc == 0) {
			bufc = r.read(buf, 0, BUFSIZE);
			if(bufc == -1) {
				bufc = 0;
				return;
			}
		}
	}
	
	private boolean pumpBuf() throws IOException {
		if(bufi == bufc) {
			fillBuf();
		}
		return bufc != 0;
	}
	
	private boolean isDelimiter(char c) {
		return c == ' ' || c == '\t' || c == '\n' || c == '\r' || c == '\f';
	}
	
	private void eatDelimiters() throws IOException {
		while(true) {
			if(bufi == bufc) {
				fillBuf();
				if(bufc == 0) throw new RuntimeException("IO: Out of input.");
			}
			
			if(!isDelimiter(buf[bufi])) break;
			++bufi;
		}
	}
	
	public String next() {
		try {
			sb.setLength(0);
			
			eatDelimiters();
			int start = bufi;
			
			while(true) {
				if(bufi == bufc) {
					sb.append(buf, start, bufi - start);
					fillBuf();
					start = 0;
					if(bufc == 0) break;
				}
				
				if(isDelimiter(buf[bufi])) break;
				++bufi;
			}
			
			sb.append(buf, start, bufi - start);
			
			return sb.toString();
		} catch(IOException e) {
			throw new RuntimeException("IO.next: Caught IOException.");
		}
	}
	
	public int nextInt() {
		try {
			int ret = 0;
			
			eatDelimiters();
			
			boolean positive = true;
			if(buf[bufi] == '-') {
				++bufi;
				if(!pumpBuf()) throw new RuntimeException("IO.nextInt: Invalid int.");
				positive = false;
			}
			
			boolean first = true;
			while(true) {
				if(!pumpBuf()) break;
				if(isDelimiter(buf[bufi])) {
					if(first) throw new RuntimeException("IO.nextInt: Invalid int.");
					break;
				}
				first = false;
				
				if(buf[bufi] >= '0' && buf[bufi] <= '9') {
					if(ret < -214748364) throw new RuntimeException("IO.nextInt: Invalid int.");
					ret *= 10;
					ret -= (int)(buf[bufi] - '0');
					if(ret > 0) throw new RuntimeException("IO.nextInt: Invalid int.");
				} else {
					throw new RuntimeException("IO.nextInt: Invalid int.");
				}
				
				++bufi;
			}
			
			if(positive) {
				if(ret == -2147483648) throw new RuntimeException("IO.nextInt: Invalid int.");
				ret = -ret;
			}
			
			return ret;
		} catch(IOException e) {
			throw new RuntimeException("IO.nextInt: Caught IOException.");
		}
	}
	
	public long nextLong() {
		try {
			long ret = 0;
			
			eatDelimiters();
			
			boolean positive = true;
			if(buf[bufi] == '-') {
				++bufi;
				if(!pumpBuf()) throw new RuntimeException("IO.nextLong: Invalid long.");
				positive = false;
			}
			
			boolean first = true;
			while(true) {
				if(!pumpBuf()) break;
				if(isDelimiter(buf[bufi])) {
					if(first) throw new RuntimeException("IO.nextLong: Invalid long.");
					break;
				}
				first = false;
				
				if(buf[bufi] >= '0' && buf[bufi] <= '9') {
					if(ret < -922337203685477580L) throw new RuntimeException("IO.nextLong: Invalid long.");
					ret *= 10;
					ret -= (long)(buf[bufi] - '0');
					if(ret > 0) throw new RuntimeException("IO.nextLong: Invalid long.");
				} else {
					throw new RuntimeException("IO.nextLong: Invalid long.");
				}
				
				++bufi;
			}
			
			if(positive) {
				if(ret == -9223372036854775808L) throw new RuntimeException("IO.nextLong: Invalid long.");
				ret = -ret;
			}
			
			return ret;
		} catch(IOException e) {
			throw new RuntimeException("IO.nextLong: Caught IOException.");
		}
	}
	
	public double nextDouble() {
		return Double.parseDouble(next());
	}
}

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: WRONG ANSWER

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: WRONG ANSWER

Test 14

Group: 3

Verdict: ACCEPTED

Test 15

Group: 3

Verdict: WRONG ANSWER