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public class Solution {
    public int findCircleNum(int[][] M) {
        if (M == null || M.length < 1 || M[0].length < 1) return 0;
        int n = M.length;
        UnionFind uf = new UnionFind(n);
        for (int i = 0; i < n; i++) {
            uf.make_set(i);
        }
        for (int i = 0; i < n; i++) {
            for (int j = 0; j <= i; j++) {
                if (M[i][j] == 1) {
                    uf.union(i, j);
                }
            }
        }
        return uf.getCount();
    }
}

class UnionFind {
    private int[] parent;
    private int[] size;
    private int n, count;
    
    public UnionFind (int n) {
        this.n = n;
        this.count = n;
        parent = new int[n];
        size = new int[n];
    }
    
    public void make_set(int x) {
        parent[x] = x;
        size[x] = 1;
    }
    
    public int find(int x) {
        // if (parent[x] != x) {
        //     parent[x] = find(parent[x]);
        // }
        while (parent[x] != x) {
            parent[x] = parent[parent[x]];
            x = parent[x];
        }
        
        return x;
    }
    
    public void union(int x, int y) {
        int parentX = find(x);
        int parentY = find(y);
        if (parentX != parentY) {
            if (size[parentX] > size[parentY]) {
                parent[parentY] = parentX;
                size[parentX] += size[parentY];
            } else {
                parent[parentX] = parentY;
                size[parentY] += size[parentX];
            }
            count--;
        } 
    }
    
    public int getCount() {
        return count;
    }
}