解决了，只需要把dis数组全初始化为负无穷
```cpp
#include<iostream>
#include<cstring>
#include<vector>
#include<queue>
using namespace std;
const int N = 5 * 1e4 + 10;
const int INF = 0x3f3f3f3f;
struct Edge {
int to;
int w;
};
vector<Edge> e[N];
int n, m;
int indegree[N];
int outdegree[N];
long long dis[N];
void topsort() { //拓扑排序
queue<int>q;
q.push(1);
dis[1] = 0;
while (q.size()) {
int t = q.front();
q.pop();
for (int i = 0; i < e[t].size(); i++) {
int j = e[t][i].to, ww = e[t][i].w;
indegree[j]--;
dis[j] = max(dis[t] + ww, dis[j]);
if (indegree[j] == 0)q.push(j);
}
}
}
int main() {
cin >> n >> m;
memset(dis,0x80,sizeof dis);
for (int i = 0; i < m; i++) {
int a; Edge ee;
cin >> a >> ee.to >> ee.w;
e[a].push_back(ee);
indegree[ee.to]++;
outdegree[a]++;
}
queue<int>q1;
//以下为排除除了1以外的入度为零的点
for (int i = 2; i <= n; i++) {
if (indegree[i] == 0)q1.push(i);
}
while (q1.size()) {
int t = q1.front();
q1.pop();
for (int i = 0; i < e[t].size(); i++) {
int j = e[t][i].to;
indegree[j]--;
if (indegree[j] == 0)q1.push(j);
}
}
topsort();
if (dis[n] < -1e5)printf("-1");
else printf("%d", dis[n]);
return 0;
}
```
by Hopoyage @ 2024-01-12 11:16:08