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;
}