BZOJ1631 [Usaco2007 Feb]Cow Party

凑数用的。。。其实是刚写了个spfa的板子，感觉很好而已。。。

每个点spfa一边就过了。。。蒟蒻都觉得水。。。

/**************************************************************
    Problem: 1631
    User: rausen
    Language: C++
    Result: Accepted
    Time:196 ms
    Memory:2380 kb
****************************************************************/
 
#include <cstdio>
#include <cstring>
#include <algorithm>
 
using namespace std;
const int N = 1005;
struct edge{
    int next, to, v;
}e[100005];
int n, m, S, X, Y, Z, tot;
int q[100005], dis[N], first[N], dis1[N], ANS;
bool v[N];
 
inline int read(){
    int x = 0, sgn = 1;
    char ch = getchar();
    while (ch < '0' || ch > '9'){
        if (ch == '-') sgn = -1;
        ch = getchar();
    }
    while (ch >= '0' && ch <= '9'){
        x = x * 10 + ch - '0';
        ch = getchar();
    }
    return sgn * x;
}
 
inline void add_edge(int x, int y, int z){
    e[++tot].next = first[x], first[x] = tot;
    e[tot].to = y, e[tot].v = z;
}
 
void spfa(int S){
    memset(dis, 127, sizeof(dis));
    q[0] = S, dis[S] = 0, v[S] = 1;
    int p, x, y;
    for (int l = 0, r = 0; l <= r; ++l){
        p = q[l];
        for (x = first[p]; x; x = e[x].next){
            y = e[x].to;
            if (dis[p] + e[x].v < dis[y]){
                dis[y] = dis[p] + e[x].v;
                if (!v[y])
                    v[y] = 1, q[++r] = y;
            }
        }
        v[p] = 0;
    }
}
 
int main(){
    n = read(), m = read(), S = read();
    for (int i = 1; i <= m; ++i){
        X = read(), Y = read(), Z = read();
        add_edge(X, Y, Z);
    }
    for (int i = 1; i <= n; ++i){
        spfa(i);
        dis1[i] = dis[S];
    }
    spfa(S);
    for (int i = 1; i <= n; ++i)
        ANS = max(ANS, dis[i] + dis1[i]);
    printf("%d
", ANS);
    return 0;
}

（p.s.  感觉做法已经很快了啊。。。那些20ms的人心态呢。。。都是怎么做的。。。）