学步园

题目已经保证会有一条可到达的路，数据中没有负环。

#include <iostream>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <queue>
#include <algorithm>

using namespace std;

const int maxn = 1010;
const int inf = 0x3f3f3f3f;

typedef struct Edge
{
        int v, w;
        Edge(int _v = 0, int _w = 0):
                v(_v), w(_w) {}
}ee;

vector<ee> e[maxn];
queue<int> q;

void add_edge(int u, int v, int w)
{
        e[u].push_back(Edge(v, w));
}

bool vis[maxn];
int cnt[maxn], dis[maxn];
int t, n;

bool SPFA(int start)
{
        while(!q.empty())
                q.pop();
        q.push(start);
        vis[start] = true;
        dis[start] = 0，cnt[start] = 1;
        int u, v;
        while(!q.empty())
        {
                u = q.front();
                q.pop();
                vis[u] = false;
                for(int i = 0; i < e[u].size(); i++)
                {
                        v = e[u][i].v;
                        if(dis[v] > dis[u] + e[u][i].w)
                        {
                                dis[v] = dis[u] + e[u][i].w;
                                if(!vis[v])
                                {
                                        vis[v] = true;
                                        q.push(v);
                                        if(++cnt[v] > n)
                                                return false;
                                }
                        }
                }
        }
        return true;
}

int main()
{
//        freopen("2387.in", "r", stdin);

        while(~scanf("%d%d", &t, &n))
        {
                memset(vis, false, sizeof(vis));
                memset(dis, 0x3f, sizeof(dis));
                memset(cnt, 0, sizeof(cnt));
                int u, v, w;
                for(int i = 0; i < t; i++)
                {
                        scanf("%d%d%d", &u, &v, &w);
                        add_edge(u, v, w);
                        add_edge(v, u, w);
                }
                if(SPFA(n))
                        printf("%d\n", dis[1]);
        }
        return 0;
}