【spfa】AcWing851.spfa求最短路——模板题
作者:互联网
AcWing851.spfa求最短路
题解
spfa算法即为Bellman-Ford的优化,只有每次dist[a]发生了变化才需要更新对应的dist[b],通过此减少循环次数
#include <iostream>
#include <cstring>
#include <queue>
using namespace std;
const int N = 1e5 + 10;
bool st[N];
int dist[N];
int h[N], e[N], v[N], ne[N], idx;
int n, m;
void add(int a, int b, int w)
{
ne[idx] = h[a], h[a] = idx, e[idx] = b, v[idx++] = w;
}
void spfa()
{
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; i = ne[i])
if(dist[e[i]] > dist[t] + v[i])
{
dist[e[i]] = dist[t] + v[i];
if(!st[e[i]]) q.push(e[i]), st[e[i]] = true ;
}
}
}
int main()
{
memset(dist, 0x3f, sizeof dist);
memset(h, -1, sizeof h);
cin >> n >> m;
int a, b, c;
for(int i = 0; i < m; ++i)
{
cin >> a >> b >> c;
add(a, b, c);
}
spfa();
if(dist[n] == 0x3f3f3f3f) cout << "impossible" << endl;
else cout << dist[n] << endl;
return 0;
}
标签:dist,idx,int,ne,st,spfa,AcWing851,模板 来源: https://www.cnblogs.com/czy-algorithm/p/16324012.html