这段循环读取完之后就报错了
是为什么啊?之前这样写一直都没事的
#include<iostream>
#include<vector>
#include<queue>
#include<cstring>
using namespace std;
const int N = 2e5+10, INF = 0x3f3f3f3f;
int dist[N], n;
bool st[N];
vector<int>g[N];
void bfs(int s)
{
queue<int>q;
int i;
memset(dist, 0x3f, sizeof dist);
for (i = 1; i<=n; i++) st[i] = false;
dist[s] = 0;
st[s] = true;
q.push(s);
while(q.size()>0)
{
int u = q.front(); q.pop();
int v;
for (i = 0; i<g[u].size(); i++)
{
v = g[u][i];
if (st[v]) continue;
st[v] = true;
dist[v] = dist[u]+1;
q.push(v);
}
}
}
int main()
{
int i, j, a, b, t;
scanf("%d", &t);
while(t--)
{
scanf("%d", &n);
for (i = 1; i<=n; i++) g[i].clear();
for (i = 1; i<=n; i++)
{
scanf("%d %d", &a, &b);
g[a].push_back(b);
g[b].push_back(a);
}
int s;
bool f = true;
for (i = 1; i<=n; i++)
if (g[i].size() != 2)
{
printf("NO\n");
f = false;
break;
}
if (!f) continue;
s = 1;
while(g[s][0] == g[s][1]) s++;
bfs(s);
for (i = 1; i<=n; i++)
{
if (dist[i]>n/2&&dist[i]<1e9)
{
printf("NO\n");
f = false;
break;
}
if (dist[i]>=1e9)
{
if(g[i][0] != g[i][1])
{
printf("NO\n");
f = false;
break;
}
}
}
if (f) printf("YES\n");
}
}