1 /*
2 差分约束系统可以做
3
4 dijkstra+ priority_queue 600+ms
5 */
6
7 // include file
8 #include <cstdio>
9 #include <cstdlib>
10 #include <cstring>
11 #include <cmath>
12 #include <cctype>
13 #include <ctime>
14
15 #include <iostream>
16 #include <sstream>
17 #include <fstream>
18 #include <iomanip>
19 #include <bitset>
20
21 #include <algorithm>
22 #include <string>
23 #include <vector>
24 #include <queue>
25 #include <set>
26 #include <list>
27 #include <functional>
28
29 using namespace std;
30
31 // typedef
32 typedef long long LL;
33 typedef unsigned long long ULL;
34 typedef __int64 Bint;
35
36 //
37 #define read freopen("in.txt","r",stdin)
38 #define write freopen("out.txt","w",stdout)
39 #define FORi(a,b,c) for(int i=(a);i<(b);i+=c)
40 #define FORj(a,b,c) for(int j=(a);j<(b);j+=c)
41 #define FORk(a,b,c) for(int k=(a);k<(b);k+=c)
42 #define FORp(a,b,c) for(int p=(a);p<(b);p+=c)
43 #define FORii(a,b,c) for(int ii=(a);ii<(b);ii+=c)
44 #define FORjj(a,b,c) for(int jj=(a);jj<(b);jj+=c)
45 #define FORkk(a,b,c) for(int kk=(a);kk<(b);kk+=c)
46
47 #define FF(i,a) for(int i=0;i<(a);i++)
48 #define FFD(i,a) for(int i=(a)-1;i>=0;i--)
49
50 #define Z(a) (a<<1)
51 #define Y(a) (a>>1)
52
53 const double eps = 1e-6;
54 const double INFf = 1e10;
55 const int INFi = 1000000000;
56 const double Pi = acos(-1.0);
57
58 template<class T> inline T sqr(T a){return a*a;}
59 template<class T> inline T TMAX(T x,T y)
60 {
61 if(x>y) return x;
62 return y;
63 }
64 template<class T> inline T TMIN(T x,T y)
65 {
66 if(x<y) return x;
67 return y;
68 }
69 template<class T> inline void SWAP(T &x,T &y)
70 {
71 T t = x;
72 x = y;
73 y = t;
74 }
75 template<class T> inline T MMAX(T x,T y,T z)
76 {
77 return TMAX(TMAX(x,y),z);
78 }
79
80
81 // code begin
82 // 30000个点 150000条边
83 #define MAXN 30010
84 struct node1
85 {
86 int s;
87 int e;
88 int p;
89 int next;
90 };
91 struct node2
92 {
93 int next;
94 };
95 struct node3
96 {
97 node3(){};
98 node3(int a,int b){
99 dx=a;
100 val=b;
101 }
102 int dx;
103 int val;
104 friend bool operator<(node3 a,node3 b)
105 {
106 return a.val>b.val;
107 }
108 };
109 node1 mem[MAXN*5];
110 node2 G[MAXN];
111 int N,M;
112 int dst[MAXN];
113 bool used[MAXN];
114 priority_queue<node3> pqn;
115
116 void SP_dijkstra()
117 {
118 while(!pqn.empty()) pqn.pop();
119 memset(used,0,sizeof(used));
120 FORi(1,N+1,1)
121 {
122 dst[i] = INFi;
123 }
124 dst[1] = 0;
125 pqn.push(node3(1,0));
126 int dx;
127 while(!pqn.empty())
128 {
129 node3 cur = pqn.top();
130 pqn.pop();
131 if( used[cur.dx] )
132 continue;
133 used[ cur.dx ]=1;
134 dx = G[cur.dx].next;
135 while(dx!=-1)
136 {
137 if( dst[cur.dx]+mem[dx].p<dst[ mem[dx].e ] )
138 {
139 dst[mem[dx].e] = dst[cur.dx] + mem[dx].p;
140 pqn.push(node3(mem[dx].e,dst[mem[dx].e]));
141 }
142 dx = mem[dx].next;
143 }
144 }
145 printf("%d\n",dst[N]);
146 }
147
148 int main()
149 {
150 read;
151 write;
152 int a,b,c;
153 scanf("%d %d",&N,&M);
154 FORi(1,N+1,1)
155 {
156 G[i].next = -1;
157 }
158 FORi(0,M,1)
159 {
160 scanf("%d %d %d",&a,&b,&c);
161 mem[i].s =a;
162 mem[i].e =b;
163 mem[i].p =c;
164
165 mem[i].next = G[a].next;
166 G[a].next = i;
167 }
168 SP_dijkstra();
169 return 0;
170 }
