POJ 2186
题目大意
暂无
题目解法
暂无
RTFC
#include <cstdio>
inline int min(int a, int b) { return a < b ? a : b; }
int head[10010], next[50010], to[50010], ecnt;
int dfn[10010], low[10010], stk[10010], scc[10010], top, idx, scccnt;
bool instk[10010];
int deg[10010];
inline void addEdge(int f, int t)
{
ecnt++;
next[ecnt] = head[f];
head[f] = ecnt;
to[ecnt] = t;
}
void tarjan(int x)
{
dfn[x] = low[x] = ++idx;
instk[stk[top++] = x] = true;
for (int cur = head[x]; cur; cur = next[cur])
if (!dfn[to[cur]])
tarjan(to[cur]), low[x] = min(low[x], low[to[cur]]);
else if (instk[to[cur]])
low[x] = min(low[x], dfn[to[cur]]);
if (dfn[x] == low[x])
{
scccnt++;
do
{
top--;
scc[stk[top]] = scccnt;
instk[stk[top]] = false;
} while (stk[top] != x);
}
}
int main()
{
int n, m;
scanf("%d%d", &n, &m);
for (int i = 0, x, y; i < m; i++)
{
scanf("%d%d", &x, &y);
addEdge(x, y);
}
for (int i = 1; i <= n; i++)
if (!dfn[i])
tarjan(i);
for (int i = 1; i <= n; i++)
for (int cur = head[i]; cur; cur = next[cur])
if (scc[i] != scc[to[cur]])
deg[scc[i]]++;
int zcnt = 0, id = 0;
for (int i = 1; i <= scccnt; i++)
if (deg[i] == 0)
zcnt++, id = i;
if (zcnt != 1)
putchar('0');
else
{
int ans = 0;
for (int i = 1; i <= n; i++)
if (scc[i] == id)
ans++;
printf("%d", ans);
}
return 0;
}