强连通,缩点后出度为0的点排序输出即可。
#include <cstdio>
#include <cstring>
#include <vector>
#include <algorithm>
using namespace std;
const int MAXN = 5010;
const int MAXM = MAXN * MAXN;
struct Edge
{
int v, next;
}edge[MAXM];
int edgeNumber, head[MAXN];
int dfn[MAXN], low[MAXN];
int n, m;
int stack[MAXN], top;
bool inStack[MAXN];
int timeStamp;
vector<int> component[MAXN];
int componentNumber;
int belong[MAXN];
vector<int> ans;
void addEdge(int u, int v)
{
edge[edgeNumber].v = v;
edge[edgeNumber].next = head[u];
head[u] = edgeNumber ++;
}
void dfs(int x)
{
dfn[x] = low[x] = timeStamp ++;
stack[top++] = x;
inStack[x] = true;
for(int i=head[x];i!=-1;i=edge[i].next)
{
int v = edge[i].v;
if(dfn[v] == -1)
{
dfs(v);
if(low[x] > low[v])
{
low[x] = low[v];
}
}
else if(inStack[v])
{
if(low[x] > dfn[v])
{
low[x] = dfn[v];
}
}
}
if(low[x] == dfn[x])
{
do
{
component[componentNumber].push_back(stack[-- top]);
inStack[stack[top]] = false;
belong[stack[top]] = componentNumber;
}
while(stack[top] != x);
++ componentNumber;
}
}
void tarjan()
{
memset(dfn, -1, sizeof(dfn));
memset(stack, -1, sizeof(stack));
memset(inStack, false, sizeof(inStack));
top = 0;
timeStamp = 0;
componentNumber = 0;
for(int i=0;i<n;++i)
{
component[i].clear();
}
for(int i=1;i<=n;++i)
{
if(dfn[i] == -1)
{
dfs(i);
}
}
ans.clear();
for(int i=0;i<componentNumber;++i)
{
bool valid = true;
for(int j=0;j<component[i].size() && valid;++j)
{
int u = component[i][j];
for(int k = head[u];k!=-1;k=edge[k].next)
{
int v = edge[k].v;
if(belong[v] != belong[u])
{
valid = false;
break;
}
}
}
if(valid)
{
for(int j=0;j<component[i].size();++j)
{
ans.push_back(component[i][j]);
}
}
}
sort(ans.begin(), ans.end());
}
int main()
{
int u, v;
while(scanf("%d", &n), n)
{
scanf("%d", &m);
edgeNumber = 0;
memset(head, -1, sizeof(head));
for(int i=0;i<m;++i)
{
scanf("%d%d", &u, &v);
addEdge(u, v);
}
tarjan();
for(int i=0;i<ans.size();++i)
{
if(i)
{
printf(" ");
}
printf("%d", ans[i]);
}
printf("\n");
}
return 0;
}
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