1 /************************************************************** 2     Problem: 1631 3     User: rausen 4     Language: C++ 5     Result: Accepted 6     Time:196 ms 7     Memory:2380 kb 8 ****************************************************************/ 9  10 #include <cstdio>11 #include <cstring>12 #include <algorithm>13  14 using namespace std;15 const int N = 1005;16 struct edge{17     int next, to, v;18 }e[100005];19 int n, m, S, X, Y, Z, tot;20 int q[100005], dis[N], first[N], dis1[N], ANS;21 bool v[N];22  23 inline int read(){24     int x = 0, sgn = 1;25     char ch = getchar();26     while (ch < ‘0‘ || ch > ‘9‘){27         if (ch == ‘-‘) sgn = -1;28         ch = getchar();29     }30     while (ch >= ‘0‘ && ch <= ‘9‘){31         x = x * 10 + ch - ‘0‘;32         ch = getchar();33     }34     return sgn * x;35 }36  37 inline void add_edge(int x, int y, int z){38     e[++tot].next = first[x], first[x] = tot;39     e[tot].to = y, e[tot].v = z;40 }41  42 void spfa(int S){43     memset(dis, 127, sizeof(dis));44     q[0] = S, dis[S] = 0, v[S] = 1;45     int p, x, y;46     for (int l = 0, r = 0; l <= r; ++l){47         p = q[l];48         for (x = first[p]; x; x = e[x].next){49             y = e[x].to;50             if (dis[p] + e[x].v < dis[y]){51                 dis[y] = dis[p] + e[x].v;52                 if (!v[y])53                     v[y] = 1, q[++r] = y;54             }55         }56         v[p] = 0;57     }58 }59  60 int main(){61     n = read(), m = read(), S = read();62     for (int i = 1; i <= m; ++i){63         X = read(), Y = read(), Z = read();64         add_edge(X, Y, Z);65     }66     for (int i = 1; i <= n; ++i){67         spfa(i);68         dis1[i] = dis[S];69     }70     spfa(S);71     for (int i = 1; i <= n; ++i)72         ANS = max(ANS, dis[i] + dis1[i]);73     printf("%d\n", ANS);74     return 0;75 }