The end of "bzoj3036" mung bean Frog

Title Description

With the new version of Baidu space offline, blog pet mung Bean Frog completed its mission, to find its new destination.

A connected graph with a direction-free loop is given, where the starting point is 1 and the end is N, and each edge has a length. The mung bean frog starts from the starting point and goes to the end.
At each vertex, if there is a road where K leaves the point, the mung bean Frog can choose any route to leave the point, and the probability of going to each road is 1/k.
Now mung bean frog want to know, from the starting point to the end of the path through the total length of the expectation is what?

Input

First line: Two integers n m, representing n points, M edges in the graph
The second line to line 1+m: 3 integers a b c each line, representing a to B with a length of C with a forward edge

Output

The expected value of the total length from the starting point to the end path, rounding retains two decimal places.

Sample input

4 4
1 2 1
1 3 2
2 3 3
3 4 4

Sample output

7.00

Tips

For 100% of data n<=100000,m<=2*n

SolvingExpect DP water problems together. F[i] represents the desired length from I to N (a forward loop-free connected graph). Be careful except for 0.

1#include <cstdio>2 #defineN 1000013 intHead[n], To[n <<2], Val[n <<2], Next[n <<2], CNT, out[N], vis[n];4 DoubleF[n];5 voidAddintXintYintz)6 {7TO[++CNT] =y;8VAL[CNT] =Z;9NEXT[CNT] =Head[x];TenHEAD[X] =CNT; One } A voidDfsintx) - { -     if(Vis[x]) the         return; -VIS[X] =1; -     inti; -      for(i = head[x]; i; i =Next[i]) +     { - DFS (To[i]); +F[X] + = F[to[i]] +Val[i]; A     } at     if( out[x]) -F[X]/= out[x]; - } - intMain () - { -     intN, m, x, Y, Z; inscanf"%d%d", &n, &m); -      while(M-- ) to     { +scanf"%d%d%d", &x, &y, &z); - Add (x, y, z); the          out[x] + + ; *     } $Dfs1);Panax Notoginsengprintf"%.2lf\n", f[1]); -     return 0; the}

The end of "bzoj3036" mung bean Frog