bzoj1726 第二短路

一道严格次短路题，WA了一下午回家才发现bellman_ford中的vis [ o ] = false 写成了 vis [ S ] = false.被自己脑残了一脸。。。。

#include<climits>
#include<cstdio>
#include<algorithm>
#include<queue>
using namespace std ; 

void min_equal ( int & a , const int b ) {
    if ( a > b ) a = b ; 
}

const int MAXN = 10000 + 20 ; 
const int MAXR = 1000000 + 20 ; 

struct edge { 
    int dis ;
    int p ;
    edge * next ; 
} ;

edge * V [ MAXN ] ;
edge E [ MAXR * 2 ] ; 

void add_edge ( const int a , const int b , const int dis ) {
    static edge * t = E ; 
    edge * x = t ++ , * y = t ++ ; 
    x -> dis = y -> dis = dis ; 
    x -> p = b ; y -> p = a ; 
    x -> next = V [ a ] ; y -> next = V [ b ] ; 
    V [ a ] = x ; V [ b ] = y ; 
}

int N , R ; 
int dis1 [ MAXN ] ; 
int dis2 [ MAXN ] ; 

void bellman_ford ( const int S , const int T , int dis [] ) {
    static int vis [ MAXN ] ;
    static const int INF = INT_MAX ;
    static queue < int > q ;
    fill ( dis , dis + N + 1 , INF ) ; 
    fill ( vis , vis + N + 1 , 0 ) ; 
    dis [ S ] = 0 ;
    vis [ S ] = true ;
    q . push ( S ) ; 
    while ( ! q . empty () ) {
        const int o = q . front () ; 
        q . pop () ; 
        vis [ o ] = false ;
        for ( edge * v = V [ o ] ; v != 0 ; v = v -> next ) 
        if ( dis [ o ] + v -> dis < dis [ v -> p ] ) {
            dis [ v -> p ] = dis [ o ] + v -> dis ; 
            if ( ! vis [ v -> p ] ) {
                vis [ v -> p ] = true ; 
                q . push ( v -> p ) ; 
            }
        }
    }
}

int main () {
    scanf ( "%d%d" , & N , & R ) ; 
    while ( R -- ) {
        int a , b , c ; 
        scanf ( "%d%d%d" , & a , & b , & c ) ; 
        add_edge ( a , b , c ) ; 
    }
    bellman_ford ( 1 , N , dis1 ) ; 
    bellman_ford ( N , 1 , dis2 ) ; 
    int ans = INT_MAX ;
    for ( int i = 1 ; i <= N ; ++ i ) 
        for ( edge * v = V [ i ] ; v != 0 ; v = v -> next ) {
            const int a = dis1 [ i ] + v -> dis + dis2 [ v -> p ] ;
            if ( a != dis1 [ N ] ) min_equal ( ans , a ) ; 
        }
    printf ( "%d
" , ans ) ;
    return 0 ;     
}