365天挑战LeetCode1000题——Day 044 按公因数计算最大组件大小 并查集

952. 按公因数计算最大组件大小

代码实现（部分看题解）

这题我想两两求公因数，但是不行，很奇怪，反而是答案看上去笨笨的枚举可以。

class DisjointSet {
    
private:
    std::vector<int> parent;
    std::vector<int> rank; // 秩
    int maxSetNum;

public:
    DisjointSet(int max_size) : parent(std::vector<int>(max_size)), rank(std::vector<int>(max_size, 1)), maxSetNum(1) {
    
        for (int i = 0; i < max_size; ++i) parent[i] = i;
    }
    
    int find(int x) {
    
        return x == parent[x] ? x : (parent[x] = find(parent[x]));
    }
    
    void _union(int x1, int x2) {
    
        int f1 = find(x1);
        int f2 = find(x2);
        if (f1 == f2) return;
        if (rank[f1] > rank[f2]) {
    
            parent[f2] = f1;
            rank[f1] += rank[f2];
            maxSetNum = max(maxSetNum, rank[f1]);
    	}
        else {
    
            parent[f1] = f2;
            rank[f2] += rank[f1];
            maxSetNum = max(maxSetNum, rank[f2]);
        }
    }
    
    bool is_same(int e1, int e2) {
    
        return find(e1) == find(e2);
    }
    
    int getHighestRank() {
    
    	return maxSetNum;
	}
};

class Solution {
    
public:
    int largestComponentSize(vector<int>& nums) {
    
    	int n = *max_element(nums.begin(), nums.end());
        DisjointSet ds(n + 1);
        for (int num : nums) {
    
        	for (int j = 2; j * j <= num; j++) {
    
                if (num % j == 0) {
    
                    ds._union(num, num / j);
                    ds._union(num, j);
                }
            }
		}
        vector<int> counts(n + 1);
        int root = 0, ans = 0;
        for (int num : nums) {
    
            root = ds.find(num);
            counts[root]++;
            ans = max(ans, counts[root]);
        }
		return ans;
    }
};