1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
| #include <bits/stdc++.h>
#define x first
#define y second
#define x1 X1
#define x2 X2
#define y1 Y1
#define y2 Y2
#define mp make_pair
#define pb push_back
using namespace std;
typedef long long LL;
typedef pair<int, int> pii;
template <typename T> inline int Chkmax (T &a, T b) { return a < b ? a = b, 1 : 0; }
template <typename T> inline int Chkmin (T &a, T b) { return a > b ? a = b, 1 : 0; }
namespace pb_ds
{
namespace io
{
const int MaxBuff = 1 << 15;
const int Output = 1 << 24;
char B[MaxBuff], *S = B, *T = B;
#define getc() ((S == T) && (T = (S = B) + fread(B, 1, MaxBuff, stdin), S == T) ? 0 : *S++)
char Out[Output], *iter = Out;
inline void flush()
{
fwrite(Out, 1, iter - Out, stdout);
iter = Out;
}
}
template<class Type> inline Type read()
{
using namespace io;
register char ch; register Type ans = 0; register bool neg = 0;
while(ch = getc(), (ch < '0' || ch > '9') && ch != '-') ;
ch == '-' ? neg = 1 : ans = ch - '0';
while(ch = getc(), '0' <= ch && ch <= '9') ans = ans * 10 + ch - '0';
return neg ? -ans : ans;
}
};
using namespace pb_ds;
const int Maxn = 4e5 + 100, Maxm = 2e6 + 100;
const LL inf = (LL)0x3f3f3f3f3f3f3f3f;
int N, M, e, Begin[Maxn], To[Maxm], Next[Maxm], W[Maxm];
inline void add_edge (int x, int y, int z)
{
To[++e] = y;
Next[e] = Begin[x];
Begin[x] = e;
W[e] = z;
}
struct node
{
int a;
LL b;
bool operator < (const node &x) const
{
return x.b < b;
}
};
priority_queue <node> Q;
LL Dis[Maxn];
int Vis[Maxn], cnt;
inline void Dijkstra(int S)
{
for (int i = 1; i < Maxn; ++i) Dis[i] = inf;
Dis[S] = 0;
Q.push((node){S, 0});
while (!Q.empty())
{
node tmp = Q.top(); Q.pop();
int x = tmp.a;
if (Vis[x]) continue;
Vis[x] = 1;
for (int i = Begin[x]; i; i = Next[i])
{
int y = To[i];
if (Dis[y] > Dis[x] + W[i])
{
Dis[y] = Dis[x] + W[i];
Q.push((node){y, Dis[y]});
}
}
}
}
struct edge
{
int x, y, z, id;
bool operator < (const edge &a) const
{
if (x == a.x) return z < a.z;
return x < a.x;
}
}E[Maxm];
int main()
{
#ifndef ONLINE_JUDGE
freopen("illness.in", "r", stdin);
freopen("illness.out", "w", stdout);
#endif
N = read<int>(), M = read<int>();
int S = Maxn - 10;
for (int i = 1; i <= M; ++i)
{
int x = read<int>(), y = read<int>(), z = read<int>();
add_edge (i, i + M, z);
add_edge (i + M, i, z);
if (x == 1) add_edge (S, i, z), add_edge (i, S, z);
else if (y == 1) add_edge (S, i + M, z), add_edge (i + M, S, z);
E[i * 2 - 1].x = x, E[i * 2 - 1].y = y, E[i * 2 - 1].z = z, E[i * 2 - 1].id = i;
E[i * 2].x = y, E[i * 2].y = x, E[i * 2].z = z, E[i * 2].id = i + M;
}
sort(E + 1, E + 2 * M + 1);
int j = 1;
for (int i = 1; i <= N; ++i)
{
if (E[j].x > i) continue;
while (E[j + 1].x == i)
{
add_edge (E[j].id, E[j + 1].id, E[j + 1].z - E[j].z);
add_edge (E[j + 1].id, E[j].id, 0);
++j;
}
++j;
}
Dijkstra(S);
LL ans = inf;
for (int i = 1; i <= 2 * M; ++i) if (E[i].x == N || E[i].y == N) Chkmin(ans, Dis[E[i].id] + E[i].z);
cout<<ans<<endl;
return 0;
}
|