Grid Teleportation Traversal

Problem

TC : vlogv, where v = m*n

class Solution {
    public int minMoves(String[] matrix) {
        int m = matrix.length;
        int n = matrix[0].length();

        int distance[][] = new int[m][n];
        for(int v[]: distance){
            Arrays.fill(v,Integer.MAX_VALUE);
        }

        Set<String> set = new HashSet<>();// to keep track of distance teleportation cells
        Map<String,List<int[]>> map = new HashMap<>(); // teleportation cells for a given cell [A-Z]
        for(int i =0;i< m;i++){
            for(int j = 0;j<n;j++){
                String str = String.valueOf(matrix[i].charAt(j));
                if(isChar(str)){
                    map.putIfAbsent(str, new ArrayList<>());
                    map.get(str).add(new int[]{i,j});
                }
            }
        }

        int dirs[][] = {{0,-1},{0,1},{-1,0},{1,0}};
        // we have to use dijkstras because the teleportation keeps the moves same
        Queue<Tuple> q = new PriorityQueue<>((a,b)-> Integer.compare(a.c, b.c));
        distance[0][0] = 0;//initial distance
        q.add(new Tuple(0,0,0));
        while(!q.isEmpty()){
            Tuple t  = q.remove();
            if(t.i == m-1 && t.j == n-1) return t.c;
            String str = String.valueOf(matrix[t.i].charAt(t.j));
            if(isChar(str) && !set.contains(str)){
                set.add(str);
                for(int c[] : map.get(str)){
                    if(distance[c[0]][c[1]] > t.c){
                        distance[c[0]][c[1]] = t.c;
                        q.add(new Tuple(c[0],c[1],t.c));
                    }
                }
            }
            for(int dir[] : dirs){
                int i = t.i + dir[0];
                int j = t.j + dir[1];

                if(i<m && j<n && i>=0 && j>=0 && !String.valueOf(matrix[i].charAt(j)).equals("#")){
                    if(distance[i][j] > t.c +1){
                        distance[i][j] = t.c + 1;
                         q.add(new Tuple(i,j, t.c+1));
                    }
                }
            }
        }
        return -1;
    }
    public boolean isChar(String s){
        if(s.equals("#") || s.equals(".")) return false;
        return true;
    }
}
class Tuple{
    int i;
    int j;
    int c;
    public Tuple(int i, int j, int c){
        this.i = i;
        this.j = j;
        this.c = c;
    }
}