【题解】P1171 售货员的难题

Tags

搜索，状压​。

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裸的旅行商问题

#include <stdio.h>
#include <string.h>
#define re register
#define GC getchar()
#define Clean(X,K) memset(X,K,sizeof(X))
#define U unsigned
#define Min(X,Y) (X<Y?X:Y)
short Qread () {
    short X = 0 ;
    char C = GC ;
    while (C > '9' || C < '0') C = GC ;
    while (C >='0' && C <='9') {
        X = X * 10 + C - '0' ;
        C = GC ;
    }
    return X ;
}
const short Maxn = 20 , INF = (1 << 15) - 1;
U short int A[Maxn][Maxn] , N ;
short F[Maxn][1 << Maxn];
void DFS (short Now , U X) {
    if (F[Now][X] != -1) return ;
    F[Now][X] = INF;
    for (re int i = 0 ; i < N; ++ i) {
        if ((X & (1 << i)) && Now != i) {
            DFS (i , X & (~ (1 << Now))) ;
            F[Now][X] = Min (F[Now][X] , A[i][Now] + F[i][X & (~ (1 << Now))]) ;
        }
    }
}
int main () {
    //freopen ("P1171.in" , "r" , stdin) ;
    N = Qread () ;
    for (re int i = 0 ; i < N; ++ i) for (re int j = 0 ; j < N; ++ j) A[i][j] = Qread () ;
    Clean (F , -1) ;
    F[0][1] = 0 ;
    for (re int i = 0 ; i < N; ++ i) DFS (i , (1 << N) - 1) ;
    int Ans = INF ;
    for (re int i = 0 ; i < N; ++ i) Ans = Min (Ans ,A[i][0] + F[i][(1 << N) - 1]) ;
    printf ("%d
" , Ans) ;
    fclose (stdin) , fclose (stdout) ;
    return 0 ;
}