c/c++语言开发共享BZOJ2763: [JLOI2011]飞行路线(分层图 最短路)

题意

sol

分层图+最短路

建(k+1)层图，对于边((u, v, w))，首先在本层内连边权为(w)的无向边，再各向下一层对应的节点连边权为(0)的有向边

如果是取最大最小值的话可以考虑二分答案+最短路

// luogu-judger-enable-o2 // luogu-judger-enable-o2 #include<bits/stdc++.h> #define pair pair<int, int> #define mp make_pair  #define fi first #define se second  using namespace std; const int maxn = 2e5 + 10; inline int read() {     char c = getchar(); int x = 0, f = 1;     while(c < '0' || c > '9') {if(c == '-') f = -1; c = getchar();}     while(c >= '0' && c <= '9') x = x * 10 + c - '0', c = getchar();     return x * f; } int n, m, k, s, t, tt, vis[maxn], dis[maxn]; vector<pair> v[maxn]; void addedge(int x, int y, int z, int f) {     v[x].push_back(mp(y, z));     if(f) v[y].push_back(mp(x, z)); } void dij(int s) {     priority_queue<pair> q; q.push(mp(0, s));     memset(dis, 0x3f, sizeof(dis)); dis[s] = 0;     while(!q.empty()) {         if(vis[q.top().se]) {q.pop(); continue;}         int p = q.top().se; q.pop(); vis[p] = 1;         for(int i = 0; i < v[p].size(); i++) {             int to = v[p][i].fi, w = v[p][i].se;             if(dis[to] > dis[p] + w) dis[to] = dis[p] + w, q.push(mp(-dis[to], to));         }     } } int main() { //  freopen("a.in", "r", stdin);     n = read(); m = read(); k = read(); s = read() + 1; t = read() + 1; tt = n * (k + 1) + 1;     for(int i = 1; i <= m; i++) {         int u = read() + 1, v = read() + 1, w = read();         for(int j = 0; j < k; j++) {             addedge(j * n + u, j * n + v, w, 1);             addedge(j * n + u, (j + 1) * n + v, 0, 0);             addedge(j * n + v, (j + 1) * n + u, 0, 0);         }         addedge(n * k + u, n * k + v, w, 1);     }     for(int j = 0; j <= k; j++) addedge(j * n + t, tt, 0, 0);     dij(s);     printf("%d", dis[tt]);     return 0; }