spfa
作者:
ysc
,
2021-07-29 12:30:11
,
所有人可见
,
阅读 315
#include <iostream>
#include <algorithm>
#include <cstring>
#include <queue>
using namespace std;
const int N = 1e5+10;
int n, m;
int h[N], e[N], ne[N], w[N], idx;
int dist[N];
bool st[N];
void add(int a, int b, int c)
{
w[idx] = c, e[idx] = b, ne[idx] = h[a], h[a] = idx ++;
}
int spfa()
{
memset(dist, 0x3f, sizeof dist);
dist[1] = 0;
queue<int> q;
q.push(1);
st[1] = true;
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];
if ( !st[j] )
{
q.push(j);
st[j] = true;
}
}
}
}
if ( dist[n] == 0x3f3f3f3f ) return -1;
return dist[n];
}
int main()
{
memset(h, -1, sizeof h);
cin >> n >> m;
while ( m -- )
{
int a, b, c;
cin >> a >> b >> c;
add(a, b, c);
}
int t = spfa();
if ( t == -1 ) puts("impossible");
else cout << t << endl;
return 0;
}