uva11324(tarjan缩点 ＋ DAG图上的简单dp)

#include <iostream>
#include <stack>
#include <vector>
#include <cstdio>
#include <cstring>
using namespace std;
const int maxn = 1e3 + 10;
int low[maxn],pre[maxn],sccno[maxn];
int scc_cnt,dfs_colok;
stack<int> s;
vector<int> G[maxn],mp[maxn];
void dfs(int u){
low[u] = pre[u] = ++dfs_colok;
s.push(u);
for (int i = 0;i < G[u].size();++i){
int v = G[u][i];
if (!pre[v]){
dfs(v);
low[u] = min(low[v],low[u]);
}else if (!sccno[v]) low[u] = min(low[u],pre[v]);
}
if (low[u] == pre[u]){
scc_cnt++;
for (;;){
int x = s.top();
s.pop();
sccno[x] = scc_cnt;
if (x == u) break;
}
}
}
void find_scc(int n){
dfs_colok = scc_cnt = 0;
memset(sccno, 0, sizeof sccno);
memset(pre, 0,sizeof pre);
for (int i = 0;i < n;i++)
if (!pre[i]) dfs(i);
}
int val[maxn];
void build(int n){
for (int i = 1;i <= scc_cnt;i++)
mp[i].clear();
memset(val, 0,sizeof val);
for (int i = 0;i < n;i++){
val[sccno[i]]++;
// cout << val[sccno[i]] << endl;
}
for (int i = 0;i < n;i++){
for (int j = 0;j < G[i].size();j++){
int v = G[i][j];
if (sccno[i] != sccno[v]){
mp[sccno[i]].push_back(sccno[v]);
}
}
}
}
int dp[maxn];
int search(int u){
if (dp[u] != -1) return dp[u];
dp[u] = val[u];
for (int i = 0;i < mp[u].size();i++){
int v = mp[u][i];
dp[u] = max(dp[u],search(v) + val[u]);
}
// cout << dp[u] << endl;
return dp[u];
}
int main(){
// freopen("in.txt","r",stdin);
// freopen("out","w",stdout);
int n,m,t;
scanf("%d",&t);
while(t--){
scanf("%d%d",&n,&m);
for (int i = 0;i < n;i++)
G[i].clear();
int a,b;
for (int i = 1;i <= m;i++){
scanf("%d%d",&a,&b);
a--;
b--;
G[a].push_back(b);
}
find_scc(n);
// cout << "scc_cnt = " << scc_cnt << endl;
build(n);
memset(dp, -1,sizeof dp);
int ans = 0;
// for (int i = 1;i <= scc_cnt;i++)
for (int i = 0;i < n;i++)
ans = max(ans,search(sccno[i]));
printf("%d\n", ans);
}
return 0;
}