【最短路】 codeforces 449B Jzzhu and Cities

直接把火车建在图上，把所有的边加到图上，求出1号点到其他所有点的单源最短路，并记录每个点的入度。。。然后挨个检查每个火车，如果火车的路大于最短路，那么条火车路肯定是多余的。如果相等，就看入度是不是大于1，如果大于1那么这条路就是多余的。。注意最大值INF的取值不要太小。。。

#include <iostream>  #include <queue>  #include <stack>  #include <map>  #include <set>  #include <bitset>  #include <cstdio>  #include <algorithm>  #include <cstring>  #include <climits>  #include <cstdlib>#include <cmath>#define maxn 200005#define eps 1e-10#define mod 1000000009#define INF 1e17  #define lowbit(x) (x&(-x))  #define lson o<<1, L, mid  #define rson o<<1 | 1, mid+1, R  typedef long long LL;using namespace std;struct Edge{LL from, to, dist;};struct node{LL d, u;bool operator < (const node &a) const {return a.d<d;}};struct Dijstra{LL n, m;priority_queue<node> q;node tmp, now;Edge e;vector<Edge> edges;vector<LL> G[maxn];bool done[maxn];LL dis[maxn];LL in[maxn];void init(void){edges.clear();memset(in, 0, sizeof in);memset(done, 0, sizeof done);for(int i = 0; i < maxn; i++)G[i].clear();}void addedge(int from, int to, int dist){e.from = from, e.to = to, e.dist = dist;edges.push_back(e);m = edges.size();G[from].push_back(m-1);}void dijstra(int s){for(int i = 0; i <= n; i++) dis[i] = INF;dis[s] = 0;tmp.u = s, tmp.d = 0;q.push(tmp);while(!q.empty()) {now = q.top();q.pop();if(done[now.u]) continue;done[now.u] = true;int d = G[now.u].size();for(int i = 0; i < d; i++) {Edge& e = edges[G[now.u][i]];if(dis[e.to] == dis[now.u] + e.dist)in[e.to]++;if(dis[e.to] > dis[now.u] + e.dist) {dis[e.to] = dis[now.u] + e.dist;in[e.to] = 1;tmp.u = e.to, tmp.d = dis[e.to];q.push(tmp);}}}}}tmp;struct opr{LL v, dist;}op[maxn];void debug(void){for(int i = 1; i <= tmp.n; i++) {printf("%I64d\n", tmp.in[i]);}}int main(void){LL m, k, u, v, dist, ans = 0;scanf("%I64d%I64d%I64d", &tmp.n, &m, &k);for(int i = 0; i < m; i++) {scanf("%I64d%I64d%I64d", &u, &v, &dist);tmp.addedge(u, v, dist);tmp.addedge(v, u, dist);}for(int i = 0; i < k ; i++) {scanf("%I64d%I64d", &op[i].v, &op[i].dist);tmp.addedge(1, op[i].v, op[i].dist);}tmp.dijstra(1);for(int i = 0; i < k; i++) {if(op[i].dist == tmp.dis[op[i].v]) if(tmp.in[op[i].v] > 1) ans++, tmp.in[op[i].v]--;if(op[i].dist > tmp.dis[op[i].v]) ans++;}printf("%I64d\n", ans);return 0;}