leetcode261.java

public class Solution {
    public boolean validTree(int n, int[][] edges) {
        int[] nums = new int[n];
        Arrays.fill(nums, -1);

        for(int[] edge : edges){
            int x = find(nums, edge[0]);
            int y = find(nums, edge[1]);

            if(x == y)
                return false;

            nums[x] = y;
        }
        return edges.length == n - 1;
    }

    private int find(int[] nums, int i){
        if(nums[i] == -1)
            return i;
        return find(nums,nums[i]);
    }
}