852spfa判断负环
作者:
一吱小晨
,
2022-10-25 21:03:08
,
所有人可见
,
阅读 137
#include<iostream>
#include<algorithm>
#include<cstring>
#include<queue>
using namespace std;
const int N = 1e5 + 10;
int n, m;
int h[N], w[N], e[N], ne[N], idx;
int dist[N], cut[N];
bool st[N];
void add (int a, int b, int c){
e[idx] = b;
ne[idx] = h[a];
w[idx] = c;
h[a] = idx ++;
}
bool spfa(){
queue<int> q;
for (int i = 1; i <= n; i ++){
st[i] = true;
q.push(i);
}
while (q.size()){
int t = q.front();
q.pop();
st[t] = false;
for (int i = h[t]; i != -1; i = ne[i]){
int j = e[i];
if (dist[j] > dist[t] + w[i]){
dist[j] = dist[t] + w[i];
cut[j] = cut[t] + 1;
if (cut[j] >= n) return true;
if (!st[j]){
st[j] = true;
q.push(j);
}
}
}
}
return false;
}
int main(){
memset(h, -1, sizeof h);
cin >> n >> m;
for (int i = 0; i < m; i ++){
int a, b, c;
cin >> a >> b >> c;
add(a, b, c);
}
if (spfa()) puts("Yes");
else puts("No");
return 0;
}