684. Redundant Connection(並查集)

package Union_Find;

public class FindRedundantConnection_684 {
	public static void main(String[] args) {
		FindRedundantConnection_684 f=new FindRedundantConnection_684();
		int[][] edges= new int[][]{{1,2}, {1,3}, {2,3}};
		int[] res=f.findRedundantConnection(edges);
		System.out.println(res[0]+","+res[1]);
	}
	
	private int[] P;
	// 標記 邊 是否被選中
	private boolean[] isMarked;
	
	public int[] findRedundantConnection(int[][] edges) {
		P=new int[edges.length+1];
		for(int i=0;i<P.length;i++) {
			P[i]=i;
		}
		isMarked=new boolean[edges.length];
		for(int i=0;i<edges.length;i++) {
			union(edges[i][0],edges[i][1],i);
		}
		
		// 找出未被標記的邊
		for(int i=0;i<isMarked.length;i++) {
			if(!isMarked[i]) {
				return edges[i];
			}
		}
		return null;
	}
	
	private int find(int x) {
		return x==P[x]?x:(x=find(P[x]));
	}
	
	private void union(int x,int y,int i) {
		int xRoot=find(x);
		int yRoot=find(y);
		if(xRoot!=yRoot) {
			P[xRoot]=yRoot;
			isMarked[i]=true;
		}
		
	}
	

}