[USACO07NOV]Cow Relays

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map+floyed+矩阵乘法（倍增floyed）

# include <stdio.h># include <stdlib.h># include <iostream># include <algorithm># include <string.h># include <map># define IL inline# define RG register# define Fill(a, b) memset(a, b, sizeof(a))using namespace std;typedef long long ll;IL ll Read(){    RG char c = getchar(); RG ll x = 0, z = 1;    for(; c < '0' || c > '9'; c = getchar()) z = c == '-' ? -1 : 1;    for(; c >= '0' && c <= '9'; c = getchar()) x = (x << 1) + (x << 3) + c - '0';    return x * z;}map <int, int> M;int n, m, k, s, t;struct Matrix{    int a[210][210];    IL void Clear(){  Fill(a, 63);  }    IL int* operator [](RG int x){  return a[x];  }    IL Matrix operator *(RG Matrix &B){        RG Matrix C; C.Clear();        for(RG int i = 1; i <= n; i++)            for(RG int j = 1; j <= n; j++)                for(RG int k = 1; k <= n; k++)                    C[i][k] = min(C[i][k], a[i][j] + B[j][k]);        return C;    }} ans, edge;int main(RG int argc, RG char* argv[]){    edge.Clear(); ans.Clear();    k = Read(); m = Read(); s = Read(); t = Read();    if(!M[s]) s = M[s] = ++n; if(!M[t]) t = M[t] = ++n;    while(m--){        RG int w = Read(), u = Read(), v = Read();        if(!M[u]) M[u] = ++n; if(!M[v]) M[v] = ++n;        edge[M[u]][M[v]] = edge[M[v]][M[u]] = min(edge[M[u]][M[v]], w);    }    for(RG int i = 1; i <= n; i++) ans[i][i] = 0;    while(k){        if(k & 1) ans = ans * edge;        edge = edge * edge;        k >>= 1;    }    printf("%d\n", ans[s][t]);    return 0;}

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