(UVA) Getting Gold - Solution

Link to the problem: https://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&category=24&page=show_problem&problem=2597

For every position next to a trap (up, down, left, right), we need to inform the player that it is not safe to move toward. Then, the only safe solution is to come back to the previous position from where he came. The player need to find all the positions where a piece of gold is, respecting the condition above mentioned. Therefore, the solution below used Depth-First Search.


import java.io.*;
import java.util.*;

class Main {
    public static int numRows;
    public static int numCols;
    public static char[][] matrix;
    public static boolean[][] visited;
    public static int[] vi = {-1,0,0,1};
    public static int[] vj = {0,-1,1,0};
    public static int countGold;
       
    public static boolean isSafe(int currI, int currJ) {
        for (int i = 0; i < 4; i++) {
            int nextI = currI+vi[i];
            int nextJ = currJ+vj[i];
            if (matrix[nextI][nextJ] == 'T') {
                return false;
            }
        }
       
        return true;
    }
   
    public static void dfs(int currI, int currJ) {
        if (currI < 0 || currJ < 0 || currI >= numRows || currJ >= numCols || matrix[currI][currJ] == '#' || visited[currI][currJ]) {
            return;
        }
       
        if (matrix[currI][currJ] == 'G') {
            countGold++;
        }
        visited[currI][currJ] = true;
       
        if (!isSafe(currI, currJ)) {
            return;
        }
        for (int i = 0; i < 4; i++) {
            int nextI = currI+vi[i];
            int nextJ = currJ+vj[i];
            dfs(nextI, nextJ);
        }
    }
   
    public static void process() throws NumberFormatException, IOException {
        Scanner sc = new Scanner(System.in);
       
        while (sc.hasNext()) {
            numCols = sc.nextInt();
            numRows = sc.nextInt();
            matrix = new char[numRows][numCols];
            int startI = 0;
            int startJ = 0;
            for (int i = 0; i < numRows; i++) {
                String line = sc.next();
                for (int j = 0; j < numCols; j++) {
                    matrix[i][j] = line.charAt(j);
                    if (matrix[i][j] == 'P') {
                        startI = i;
                        startJ = j;
                    }
                }
            }
           
            countGold = 0;
            visited = new boolean[numRows][numCols];
            dfs(startI, startJ);
            System.out.println(countGold);
        }
       
        return;
    }
   
    public static void main(String[] args) throws NumberFormatException, IOException {
        Main m = new Main();
        m.process();
       
        System.exit(0);
    }
}