搜索模板 & 拓扑排序

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// 深度优先遍历框架
void dfs(int x) 
{
	v[x] = 1;
	for (int i = head[x]; i; i = next[i]) 
	{
		int y = ver[i];
		if (v[y]) continue;
		dfs(y);
	}
}

// DFS序
void dfs(int x) 
{
	a[++m] = x;
	v[x] = 1;
	for (int i = head[x]; i; i = next[i]) 
	{
		int y = ver[i];
		if (v[y]) continue;
		dfs(y);
	}
	a[++m] = x;
}

// 求树中各点的深度
void dfs(int x) 
{
	v[x] = 1;
	for (int i = head[x]; i; i = next[i]) 
	{
		int y = ver[i];
		if (v[y]) continue; // 点y已经被访问过了
		d[y] = d[x] + 1;
		dfs(y);
	}
}

// 求树的重心
void dfs(int x) 
{
	v[x] = 1; size[x] = 1; // 子树x的大小
	int max_part = 0; // 删掉x后分成的最大子树的大小
	for (int i = head[x]; i; i = next[i]) 
	{
		int y = ver[i];
		if (v[y]) continue; // 点y已经被访问过了
		dfs(y);
		size[x] += size[y];
		max_part = max(max_part, size[y]);
	}
	max_part = max(max_part, n - size[x]);
	if (max_part < ans) 
	{
		ans = max_part;
		pos = x;
	}
}


//求树的重心
#include <iostream>
#include <algorithm>
#include <cstring>
using namespace std;
const int N = 1e5 + 4, M = 2 * N;
int h[N], to[M], ne[M], idx;
int n, ans = 1000000;
bool v[N];
void add(int u, int v)
{
    to[idx] = v, ne[idx] = h[u], h[u] = idx ++;
}

int dfs(int u)
{
    v[u] = true;
    int sum = 0, size = 0;
    for(int i = h[u]; ~i; i = ne[i])
    {
        int j = to[i];
        if(v[j])    continue;
        int s = dfs(j);
        size = max(size, s);	//求以u为根节点的每个森林的最大大小(节点数)
        sum += s;		//以u为节点除u的树，节点数
    }
    size = max(size, n - sum - 1);		//剩下的联通部分
    ans = min(size, ans);		//最大子块求最小
    return sum + 1;			//加上u即为以u为根的树
}	

int main()
{
    int u, v;
    cin >> n;
    memset(h, -1, sizeof(h));
    for(int i = 0; i < n - 1; i ++ )
    {
        cin >> u >> v;
        add(u, v), add(v, u);
    }
    dfs(1);
    cout << ans << endl;
    return 0;
}


// 划分图的连通块
void dfs(int x) 
{
	v[x] = cnt;
	for (int i = head[x]; i; i = next[i]) 
	{
		int y = ver[i];
		if (v[y]) continue;
		dfs(y);
	}
}
for (int i = 1; i <= n; i++)
	if (!v[i]) 
	{
		cnt++;
		dfs(i);
	}

// 广度优先遍历框架
void bfs() {
	memset(d, 0, sizeof(d));
	queue<int> q;
	q.push(1); d[1] = 1;
	while (q.size()) 
	{
		int x = q.front(); q.pop();
		for (int i = head[x]; i; i = next[i]) 
		{
			int y = ver[i];
			if (d[y]) continue;
			d[y] = d[x] + 1;
			q.push(y);
		}
	}
}

// 拓扑排序
void add(int x, int y) // 在邻接表中添加一条有向边
{ 
	ver[++tot] = y, next[tot] = head[x], head[x] = tot;
	deg[y]++;
}
void topsort() 
{
	queue<int> q;
	for (int i = 1; i <= n; i++)
		if (deg[i] == 0) q.push(i);
	while (q.size()) {
		int x = q.front(); q.pop();
		a[++cnt] = x;
		for (int i = head[x]; i; i = next[i]) 
		{
			int y = ver[i];
			if (--deg[y] == 0) q.push(y);
		}
	}
}
int main() 
{
	cin >> n >> m; // 点数、边数
	for (int i = 1; i <= m; i++) {
		int x, y;
		scanf("%d%d", &x, &y);
		add(x, y);
	}
	topsort();
	for (int i = 1; i <= cnt; i++)
		printf("%d ", a[i]);
	cout << endl;
}
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