Poj 3613 cow Relays

Cow relaystime limit: 1000 msmemory limit: 65536 kbthis problem will be judged on PKU. Original ID: 3613
64-bit integer Io format: % LLD Java class name: Main

For their physical fitness program,N(2 ≤N<1,000,000) cows have decided to run a relay race usingT(2 ≤T≤ 100) cow trails throughout the pasture.

Each trail connects two different intersections (1 ≤I1I≤ 1,000; 1 ≤I2I≤ 1,000), each of which is the termination for at least two trails. The cows knowLengthiOf each Trail (1 ≤Lengthi≤ 1,000), the two intersections the trail connects, and they know that no two intersections are directly connected by two different trails. The trails form a structure known mathematically as a graph.

To run the relay,NCows position themselves at various intersections (some intersections might have more than one cow ). they must position themselves properly so that they can hand off the baton cow-by-cow and end up at the proper finishing place.

Write a program to help position the cows. Find the shortest path that connects the starting intersection (S) And the ending intersection (E) And traverses exactlyNCow trails.

Input

* Line 1: four space-separated integers:N,T,S, AndE
* Lines 2 ..T+ 1: LineI+ 1 describes trailIWith three space-separated integers:Lengthi,I1I, AndI2I

Output

* Line 1: A single integer that is the shortest distance from IntersectionSTo IntersectionEThat traverses exactlyNCow trails.

Sample Input

2 6 6 411 4 64 4 88 4 96 6 82 6 93 8 9

Sample output

10

Sourceusaco 2007 November gold solution: Fast Power of the Floyd matrix. The matrix method is good, and the matrix method is great. I don't know the Matrix Method !!!!!!!!!

 1 #include <iostream> 2 #include <cstdio> 3 #include <cstring> 4 #include <cmath> 5 #include <algorithm> 6 #include <climits> 7 #include <vector> 8 #include <queue> 9 #include <cstdlib>10 #include <string>11 #include <set>12 #include <stack>13 #define LL long long14 #define pii pair<int,int>15 #define INF 0x3f3f3f3f16 using namespace std;17 int lisan[2010],n = 0,k,t,s,e;18 struct Matrix {19     int m[210][210];20     Matrix() {21         for(int i = 0; i < 210; i++)22             for(int j = 0; j < 210; j++)23                 m[i][j] = INF;24     }25 };26 Matrix mul(Matrix &x,Matrix &y) {27     Matrix z;28     for(int k = 1; k <= n; k++){29         for(int i = 1; i <= n; i++){30             for(int j = 1; j <= n; j++)31                 z.m[i][j] = min(z.m[i][j],x.m[i][k]+y.m[k][j]);32         }33     }34     return z;35 }36 Matrix fastPow(Matrix x,int index){37     Matrix y;38     for(int i = 0; i <= n; i++) y.m[i][i] = 0;39     while(index){40         if(index&1) y = mul(y,x);41         index >>= 1;42         x = mul(x,x);43     }44     return y;45 }46 int main() {47     Matrix now;48     int w,u,v;49     scanf("%d %d %d %d",&k,&t,&s,&e);50     while(t--){51         scanf("%d %d %d",&w,&u,&v);52         if(!lisan[u]) lisan[u] = ++n;53         if(!lisan[v]) lisan[v] = ++n;54         now.m[lisan[u]][lisan[v]] = now.m[lisan[v]][lisan[u]] = w;55     }56     now = fastPow(now,k);57     printf("%d\n",now.m[lisan[s]][lisan[e]]);58     return 0;59 }

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Poj 3613 cow Relays