Graph Paths II.cpp

#include<bits/stdc++.h>
using namespace std;
#define INF 2147483647
//#define INFL 9223372036854775807
#define INFL 0x3f3f3f3f3f3f3f3f
#define pii pair<int,int>
#define F first
#define S second
#define mp make_pair
#define pb push_back
#define ll long long
#define ull unsigned long long
#define M 1000000007
#define FASTIO ios_base::sync_with_stdio(false);cin.tie(NULL); cout.tie(NULL);
#define take(x) scanf("%d",&x)
#define DE(x) printf("\ndebug %d\n",x);
#define vout(x) for(int i=0;i<x.size();i++) printf("%d ",x[i]);
#define pie acos(-1)

const int N = 105;

void mult(ll aa[][N], ll bb[][N], ll cc[][N], int n) {
    int i, j, k;

    for (i = 0; i < n; i++)
        for (j = 0; j < n; j++) {
            long long c = INFL, d;

            for (k = 0; k < n; k++)
                if (c > (d = aa[i][k] + bb[k][j]))
                    c = d;
            cc[i][j] = c;
        }
}

void power(ll aa[][N], ll pp[][N], ll tt[][N], int n, int k) {
    if (k == 0) {
        int i, j;

        for (i = 0; i < n; i++)
            for (j = 0; j < n; j++)
                pp[i][j] = i == j ? 0 : INFL;
        return;
    }
    if (k % 2 == 0) {
        power(aa, tt, pp, n, k / 2);
        mult(tt, tt, pp, n);
    } else {
        power(aa, pp, tt, n, k / 2);
        mult(pp, pp, tt, n);
        mult(tt, aa, pp, n);
    }
}

int main(){
    ll aa[N][N], pp[N][N], tt[N][N];
    int n,m,k;
    cin>>n>>m>>k;
    for(int i=0;i<n;i++) for(int j=0;j<n;j++) aa[i][j] = pp[i][j] = tt[i][j] = INFL;
    int a,b,c;
    for(int i=0;i<m;i++){
        cin>>a>>b>>c;
        a--;b--;
        if( aa[a][b]>c )
            aa[a][b] = c;
    }
    power(aa,pp,tt,n,k);
    if( pp[0][n-1] == INFL ){
        cout<<-1;
    } else{
        cout<<pp[0][n-1];
    }
}