题目链接
1 #include <bits/stdc++.h>
2 using namespace std;
3 typedef long long ll;
4 inline ll read(){
5 int x=0,f=1;char ch=getchar();
6 while(ch>'9'||ch<'0'){if(ch=='-')f=-1;ch=getchar();}
7 while(ch>='0'&&ch<='9'){x=x*10+ch-'0';ch=getchar();}
8 return x*f;
9 }
10
11 /***********************************************************/
12
13 const int maxn = 100010;
14 int n, m;
15 int dis[maxn], head[maxn], look[maxn];
16 queue<int>q;
17 int ans, cas;
18
19 struct Edge
20 {
21 int u, v, w, next, vis;
22 }edge[maxn*4];
23
24 void add_edge(int u, int v, int w){
25 edge[cas].u = u; edge[cas].v = v; edge[cas].w = w;
26 edge[cas].next = head[u]; edge[cas].vis = 0;
27 head[u] = cas++;
28 }
29
30 void dfs(int rt, int cl, int num){
31 if(rt == n) {
32 ans = num;
33 return;
34 }
35 if(!look[rt]){
36 look[rt] = 1;
37 dis[rt] = num;
38 q.push(rt);
39 }
40 for(int i = head[rt];i != -1;i = edge[i].next){
41 if(edge[i].vis) continue;
42 if(edge[i].w == cl){
43 edge[i].vis = 1;
44 dfs(edge[i].v, cl, num);
45 }
46 }
47 return;
48 }
49
50 int bfs(){
51 while(!q.empty()) q.pop();
52 q.push(1); //从一开始走
53 dis[1] = 0;
54 look[1] = 1;
55 while(!q.empty()){
56 int now = q.front(); q.pop();
57 for(int i = head[now];i != -1;i = edge[i].next){
58 if(edge[i].vis) continue; //每条边只走一次
59 int v = edge[i].v;
60 edge[i].vis = 1;
61 dfs(v, edge[i].w, dis[now]+1); //把所有与当前路径相同权值的路径加入
62 if(ans > 0) break;
63 }
64 if(ans > 0) break;
65 }
66 return ans;
67 }
68
69 void init(){
70 cas = 0;
71 memset(head, -1, sizeof(head));
72 memset(look, 0, sizeof(look));
73 memset(dis, 0x7f, sizeof(dis));
74 }
75
76 int main(){
77 while(~scanf("%d%d", &n, &m)){
78 init();
79 for(int i = 1;i <= m;i++){
80 int u, v, w;
81 u = read(); v = read(); w = read();
82 add_edge(u, v, w);
83 add_edge(v, u, w);
84 }
85 ans = -1;
86 ans = bfs();
87 printf("%d\n", ans);
88 }
89 return 0;
90 }
