洛谷训练赛 A.Misaka Network

给出一DAG，求最小多少个控制点，能够使得控制图中所有点，控制点可以控制本身和他直接能到的点

题解：只需按拓扑序控制每个点即可

#include<iostream>
#include<string>
#include<unordered_map>
#include<cmath>
#include<cstring>
#include<vector>
#include<map>
#include<set>
#include<algorithm>
#include<queue>
#include<stack>
#include<sstream>
#include<cstdio>
#define INF 0x3f3f3f3f
const int maxn = 1e5 + 15;
const double PI = acos(-1.0);
typedef long long ll;
using namespace std;


int indeg[maxn];
int topo[maxn];
int vis[maxn];
vector<int> vec[maxn];
queue<int> q;
int n, m, u, v, num;

void topsort() {
    int cnt = 0;
    while (!q.empty()) q.pop();
    num = 0;
    for (int i = 1; i <= n; i++) if (!indeg[i])  q.push(i), topo[cnt++] = i;
    while (!q.empty()) {
        int now = q.front();
        q.pop();
        num++;
        for (int i = 0; i < vec[now].size(); i++) {
            if (--indeg[vec[now][i]]==0) q.push(vec[now][i]), topo[cnt++] = vec[now][i];
        }
    }
}

int main() {
    scanf("%d%d", &n, &m);
    for (int i = 0; i < m; i++) {
        scanf("%d%d", &u, &v);
        vec[u].push_back(v);
        indeg[v]++;
    }
    topsort();
    int ans = 0;
    for (int i = 0; i < n; i++) {
        if (!vis[topo[i]]) {
            for (int j = 0; j < vec[topo[i]].size(); j++) vis[vec[topo[i]][j]]++;
            ans++;
        }
    }
    //for (int i = 0; i < n; i++) printf("%d ", topo[i]);
    printf("%d", ans);
    return 0;
}