8.16 - hard - 59

305. Number of Islands II

一道union-find的题目，这类题目只要找准谁是boss就可以了，剩下的就去套模板

class Solution(object):
    # @param {int} n an integer
    # @param {int} m an integer
    # @param {Pint[]} operators an array of point
    # @return {int[]} an integer array
    def numIslands2(self, n, m, operators):
        # Write your code here
        res = []
        self.h = {}
        self.count = 0
        
        for p in operators:
            i, j = p
            if (i, j) in self.h:
                continue
            self.count += 1
            self.h[(i, j)] = (i, j)
            for x, y in [[i-1, j], [i+1, j], [i, j-1], [i, j+1]]:
                if 0 <= x < n and 0 <= y < m and (x, y) in self.h:
                    self.union((i,j), (x,y))
            res.append(self.count)
        
        return res
            
        
    def union(self, n1, n2):
        f1 = self.find(n1)
        f2 = self.find(n2)
        if f1 != f2:
            self.h[f2] = f1
            self.count -= 1
        
    
    def find(self, n):
        if n == self.h[n]:
            return n
        self.h[n] = self.find(self.h[n])
        return self.h[n]