BiruLyu
6/22/2017 - 4:53 AM

323. Number of Connected Components in an Undirected Graph.java

public class Solution {
    public int countComponents(int n, int[][] edges) {
        UnionFind uf = new UnionFind(n);
        for (int i = 0; i < n; i++) {
            uf.make_set(i);
        }
        for (int i = 0; i < edges.length; i++) {
            uf.union(edges[i][0], edges[i][1]);
        }
        return uf.getCount();
    }
}

class UnionFind {
    private int[] parent;
    private int[] size;
    private int n, count;
    
    public UnionFind (int n) {
        this.n = n;
        this.count = 0;
        parent = new int[n];
        size = new int[n];
    }
    
    public void make_set(int x) {
        parent[x] = x;
        size[x] = 1;
        count++;
    }
    
    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 parent[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;
    }
}