算法-并查集-200

public class Solution {
    public int NumIslands(char[][] grid) {
    if(grid == null || grid.Count() == 0) return 0;
    int rowCount = grid.Count();
    int colCount = grid[0].Count();
    int waters = 0;
    UnionFind uf = new UnionFind(grid);
    for(int i=0;i<rowCount;i++)
    {
        for(int j=0;j<colCount;j++)
        {
            if(grid[i][j] == '0')
            {
                waters++;
            }else{
                int[][] direction = new int[][]{  new int[]{0,1},
                                        new int[]{0,-1},
                                        new int[]{1,0},
                                        new int[]{-1,0}
                                    };
                foreach(var dir in direction)
                {
                    int x = i + dir[0];
                    int y = j + dir[1];
                    if(x >= 0 && y >= 0 && x < rowCount && y < colCount && grid[x][y] == '1')
                    {
                        uf.Union(x*colCount+y,i*colCount+j);
                    }

                }
            }
        }
    }
    return uf.GetCount() - waters;
    }

 

}

// unionFind函数
public class UnionFind{
    private int[] root = null;
    private int count = 0;

    public UnionFind(char[][] grid)
    {
        int colCount = grid.Length;
        int rowCount = grid[0].Length;
        root = new int[colCount*rowCount];
        count = colCount*rowCount;
        for (int i = 0; i < colCount*rowCount; i++)
        {
            root[i] = i;
        }
    }

    private int Find(int x)
    {
        if (x == root[x])
        {
            return x;
        }
        return root[x] = Find(root[x]);
    }

    public void Union(int x,int y)
    {
        int rootX = Find(x);
        int rootY = Find(y);
        if (rootX != rootY) {
            root[rootX] = rootY;
            count --; 
        }
    }

    public int GetCount(){
        return count;
    }

}