并查集

class Solution {
    private class UnionFindUtil {

        // 对应父节点位置
        private int[] parent;

        // 初始化 每个元素的父节点索引==自身索引
        public UnionFindUtil(int n) {
            parent = new int[n];
            for (int i = 0; i < n; i++) {
                parent[i] = i;
            }
        }

        // 查找
        public int find(int x) {
            if (parent[x] == x) {
                return x;
            }

            // 路径压缩
            parent[x] = find(parent[x]);

            return parent[x];
        }

        // 合并
        public void union(int x, int y) {
            int rootX = find(x);
            int rootY = find(y);

            if (rootX != rootY) {
                parent[rootX] = rootY;
            }
        }
    }

    public  int largestComponentSize(int[] A) {
        int maxVal = 0;
        for (int num : A) {
            maxVal = Math.max(maxVal, num);
        }

        // 使用质数来判断是否两连
        UnionFindUtil unionFind = new UnionFindUtil(maxVal + 1);

        for (int num : A) {
            double upBound = Math.sqrt(num);
            for (int i = 2; i <= upBound; i++) {
                if (num % i == 0) {
                    unionFind.union(num, i);
                    unionFind.union(num, num / i);
                }
            }
        }

        // 找出最大者
        int[] cnt = new int[maxVal + 1];
        int res = 0;
        for (int num : A) {
            int root = UnionFindUtil.find(num);
            // 统计组先节点出现的次数 每次加一
            cnt[root]++;
            res = Math.max(res, cnt[root]);
        }
        return res;
    }

}