题目链接：https://www.luogu.org/problemnew/show/P2939
本来说是双倍经验题，跟飞行路线一样的，结果我飞行路线拿deque优化SPFA过了这里过不了了。
所以多学一种优先队列优化。
#include <queue>
#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
#define ll long long
using namespace std;
const ll maxn = 200000 + 10;
const ll inf = 2147483647;
inline ll read()
{
ll k=0,f=1;
char c=getchar();
while(!isdigit(c))
{
if(c=='-')f=-1;
c=getchar();
}
while(isdigit(c))
{
k=(k<<1)+(k<<3)+c-48;
c=getchar();
}
return k*f;
}
ll n, m, k, s, end, dis[maxn][30];
bool vis[maxn][30];
struct edge{
ll from, len, to, next;
}e[maxn<<2];
ll head[maxn], cnt = 0;
struct que{
ll a, b;
};
struct cmp{
bool operator ()(que &x, que &y)
{
return dis[x.a][x.b] > dis[y.a][y.b];
}
};
priority_queue<que, vector<que>, cmp> q;
void add(ll u, ll v, ll w)
{
e[++cnt].from = u;
e[cnt].to = v;
e[cnt].len = w;
e[cnt].next = head[u];
head[u] = cnt;
}
void SPFA()
{
memset(dis, 127, sizeof(dis));
memset(vis, 0, sizeof(vis));
q.push((que){s,0});
dis[s][0] = 0;
vis[s][0] = 1;
while(!q.empty())
{
que now = q.top(); q.pop();
vis[now.a][now.b] = 0;
for(ll i = head[now.a]; i != -1; i = e[i].next)
{
if(dis[e[i].to][now.b] > dis[now.a][now.b] + e[i].len)
{
dis[e[i].to][now.b] = dis[now.a][now.b] + e[i].len;
if(vis[e[i].to][now.b] == 0)
{
vis[e[i].to][now.b] = 1;
q.push((que){e[i].to, now.b});
}
}
if(now.b + 1 <= k)
{
if(dis[e[i].to][now.b + 1] > dis[now.a][now.b])
{
dis[e[i].to][now.b + 1] = dis[now.a][now.b];
if(vis[e[i].to][now.b + 1] == 0)
{
vis[e[i].to][now.b + 1] = 1;
q.push((que){e[i].to, now.b + 1});
}
}
}
}
}
}
int main()
{
memset(head, -1, sizeof(head));
n = read(); m = read(); k = read();
s = 1, end = n;
for(ll i = 1; i <= m; i++)
{
ll u, v, w;
u = read(); v = read(); w = read();
add(u, v, w); add(v, u, w);
}
SPFA();
printf("%lld",dis[end][k]);
return 0;
}