week 5 542. 01 Matrix

public class Solution {
    int row;
    int col;
    
    int [] dx = {1, -1, 0, 0};
    int [] dy = {0, 0, 1, -1};
    
    public List<List<Integer>> updateMatrix(List<List<Integer>> matrix){
        
        if (matrix == null || matrix.size() == 0 || matrix.get(0).size() == 0){
            return matrix;
        }
        row = matrix.size();
        col = matrix.get(0).size();
        preSet(matrix);
        
        for(int i = 0; i < row; i++){
            for(int j = 0; j < col; j++){
                if(matrix.get(i).get(j) == 1){
                    helper (matrix, 1, i, j);
                }
            }
        }
        return matirx;
    }
}
public void preSet(List<List<Integer>> matrix){
    for (int i = 0; i < row; i++){
        for (int j = 0; j < col; j++){
            
            if(matrix.get(i).get(j)==0){
                continue;
            }
            
            boolean flag = false;
            for (int k = 0; k < 4; k++){
                int x = i + dx[k];
                int y = j + dy[k];
                if (x < 0 || x >= row || y < 0 || y >= col){
                    continue;
                }
                flag |= matrix.get(x).get(y) == 0;
            }
            if(!flag){
                matrix.get(i).set(j, Integer.MAX_VALUE);
            }
                
        }
    }
}

public void helper (List<List<Integer>> matrix, int dist, int x, int y){
    if (matrix.get(x).get(y) < dist){
        return;
    }
    if(matrix.get(x).get(y) == dist && matrix.get(x).get(y) != 1){
        return;
    }
    matrix.get(x).set(y, dist);
    
    for(int i = 0; i < 4; i++){
        int xNext = x + dx[i];
        int yNext = y + dy[i];
        if(xNext < 0 || xNext >= row || yNext < 0 || yNext >= col ){
            continue;
        }
        helper(matrix, dist + 1, xNext, yNext);
    }
 }