https://leetcode-cn.com/problems/number-of-islands/

[bug]

class Solution {

    char[][] grid;
    int w, h;
    int[][] dirs = {{-1,0}, {1,0}, {0,-1}, {0,1}};
    Map<Integer, Integer> map = new HashMap<>();

    public int numIslands(char[][] grid) {

        this.grid = grid;
        int w = grid[0].length; 
        int h = grid.length;

        unionFind();
                     
        Set<Integer> rep = new HashSet<>();                      
        for(int y=0;y<h;y++){
            for(int x=0;x<w;x++){
                if(grid[y][x]==1){
                    int[] root = findRoot(y, x);
                    rep.add(toNum(root[0], root[1]));
                }
            }
        }
        return rep.size();
    }

    void unionFind(){

        for(int y=0;y<h;y++){
            for(int x=0;x<w;x++){
                if(grid[y][x]==0){
                    continue;
                }
                map.put(y*w+x, y*w+x);
                for(int[] dir:dirs){
                    int y2 = y + dir[0];
                    int x2 = x + dir[1];
                    if(grid[y2][x2]==0){
                        continue;
                    }
                    int[] root1 = findRoot(y, x);   
                    int[] root2 = findRoot(y2, x2);
                    int rep1 = toNum(root2[0], root2[1]);
                    int rep2 = toNum(root1[0], root1[1]);
                    if(rep1==rep2){
                        continue;
                    }
                    map.put(rep2, rep1);
                }
            }
        }
        
    }

    int toNum(int y, int x){
        return y*w+x;
    }

    int[] findRoot(int y, int x){
        int k = y*w + x;
        while(map.get(k)!=k){
            int v = map.get(k);
            k = v; 
        }
        int y2 = k/w;
        int x2 = k%w;
        return new int[]{y, x};
    }
}