OI-codes/S2OJ/106/data/std.cpp

#include <bits/stdc++.h>
#define R register int
#define ll long long
#define db double
#define FOR(i, j, k) for (R i = j; i <= k; i++)
#define DEC(i, j, k) for (R i = j; i >= k; i--)
#define walk(i, u) for (R i = 0; i < g[u].size(); i++)
#define visch(i, u) for (R i = head[u]; i; i = edge[i].next)
using namespace std;

inline int read() {
    int x = 0;
    bool flag = 0;
    int ch = getchar();
    while ('0' > ch || ch > '9') {
        if (ch == '-')
            flag = 1;
        ch = getchar();
    }
    while ('0' <= ch && ch <= '9') {
        x = (x << 1) + (x << 3) + (ch ^ 48);
        ch = getchar();
    }
    return flag ? -x : x;
}

const int maxn = 2510, maxm = 6210;
int n, m, s, t;

struct E {
    int to, nxt, w;
} edge[maxm << 1];

int head[maxn], ec;

inline void adde(int u, int v, int w) {
    edge[++ec].to = v;
    edge[ec].nxt = head[u];
    edge[ec].w = w;
    head[u] = ec;
}

deque<int> q;
ll dis[maxn];
bool vis[maxn];

inline void spfa() {
    FOR(i, 1, n)
    dis[i] = 0x3f3f3f3f3f3f3f3f;
    dis[s] = 0;
    vis[s] = 1;
    q.push_back(s);
    while (q.size()) {
        int u = q.front();
        q.pop_front();
        vis[u] = 0;
        for (int i = head[u]; i; i = edge[i].nxt) {
            int v = edge[i].to;
            if (dis[u] + edge[i].w < dis[v]) {
                dis[v] = dis[u] + edge[i].w;
                if (!vis[v])
                    q.push_back(v);
            }
        }
    }
}

int main() {
    n = read(), m = read(), s = read(), t = read();
    FOR(i, 1, m) {
        int x = read(), y = read(), z = read();
        adde(x, y, z);
        adde(y, x, z);
    }
    spfa();
    printf("%lld", dis[t]);
    return 0;
}