并查集

并查集(递归写法)

#include<bits/stdc++.h>
using namespace std;
const int X = 10010;
int f[X];
int n, m;	
//初始化
void init() {
	for (int i = 0; i < X; i++) {
		f[i] = i;
	}
}
//查找上级是谁
int find(int x) {
	if (x != f[x]) {
		return f[x] = find(f[x]);//路径压缩
		//相当于
		/*
		f[k]=find(f[k]);
        return f[k];
		*/
	}
	return f[x];
}
//合并
void join(int x, int y) {
	int fx = find(x), fy = find(y);
	if (fx != fy) {
		f[fy] = fx;
	}
}
//判断集合个数
bool check()
{
	int sum = 0;
	for (int i = 1; i <= n; i++)
	{
		if (f[i] == i) sum++;//统计独立集合的个数
		if (sum == 2) return 0;//发现有两个就返回false应该会省一点时间
	}
	return 1;//只有1个集合，返回true
}
int main() {
	init();
	cin >> n >> m;
	while (m--) {
		int t, x, y;
		cin >> t >> x >> y;
		if (t == 1) {
			join(x, y);
		}
		if (t == 2) {
			if (find(x) == find(y))
				cout << "Y" << endl;
			else
				cout << "N" << endl;
		}
	}
	return 0;
}

并查集（循环写法）

#include<bits/stdc++.h>
using namespace std;
const int X = 10010;
int f[X];
int ceng[X];
int n, m;
//初始化
void init() {
	for (int i = 0; i < X; i++) {
		f[i] = i;
		ceng[i] = 0;
	}
}
//查找上级是谁
int find(int x) {
	int i, j, k;
	k = x;
	while (k != f[k])
		k = f[k];
	i = x;
	while (i != k) {
		j = f[i];
		f[i] = k;
		i = j;
	}
	return k;
}
//合并
void join(int x, int y) {
	int fx = find(x), fy = find(y);
	if (ceng[fx] > ceng[fy])
		f[fy] = fx;
	else {
		if (ceng[fx] == ceng[fy])
			ceng[fy]++;
		f[fx] = fy;
	}
}
//判断集合个数
bool check()
{
	int sum = 0;
	for (int i = 1; i <= n; i++)
	{
		if (f[i] == i) sum++;//统计独立集合的个数
		if (sum == 2) return 0;//发现有两个就返回false应该会省一点时间
	}
	return 1;//只有1个集合，返回true
}	
int main() {
	init();
	cin >> n >> m;
	while (m--) {
		int t, x, y;
		cin >> t >> x >> y;
		if (t == 1) {
			join(x, y);
		}
		if (t == 2) {
			if (find(x) == find(y))
				cout << "Y" << endl;
			else
				cout << "N" << endl;
		}
	}
	return 0;
}