【题目链接】
【思路要点】
- 补档博客，无题解。
【代码】
#include<bits/stdc++.h> using namespace std; #define MAXN 505 #define INF 1e9 #define MAXQ 1000005 template <typename T> void read(T &x) { x = 0; int f = 1; char c = getchar(); for (; !isdigit(c); c = getchar()) if (c == '-') f = -f; for (; isdigit(c); c = getchar()) x = x * 10 + c - '0'; x *= f; } struct edge {int dest, flow, cost; unsigned home; }; int n, m, s, t, tot, len, flow, cost; int inp[MAXN], outp[MAXN]; int dist[MAXN], path[MAXN]; unsigned home[MAXN]; vector <edge> a[MAXN]; void flow_path() { int p = t, ans = INF; while (p != s) { ans = min(ans, a[path[p]][home[p]].flow); p = path[p]; } flow += ans, cost += ans * len; p = t; while (p != s) { a[path[p]][home[p]].flow -= ans; a[p][a[path[p]][home[p]].home].flow += ans; p = path[p]; } } bool spfa() { static int q[MAXQ]; static bool inq[MAXN]; int l = 0, r = 0; q[0] = s, inq[s] = true, dist[s] = 0; while (l <= r) { int tmp = q[l++]; inq[tmp] = false; for (unsigned i = 0; i < a[tmp].size(); i++) if (a[tmp][i].flow != 0 && dist[a[tmp][i].dest] > dist[tmp] + a[tmp][i].cost) { dist[a[tmp][i].dest] = dist[tmp] + a[tmp][i].cost; path[a[tmp][i].dest] = tmp; home[a[tmp][i].dest] = i; if (!inq[a[tmp][i].dest]) { inq[a[tmp][i].dest] = true; q[++r] = a[tmp][i].dest; } } } len = dist[t]; for (int i = 0; i <= r; i++) dist[q[i]] = INF; return len != INF; } void addedge(int s, int t, int flow, int cost) { a[s].push_back((edge) {t, flow, cost, a[t].size()}); a[t].push_back((edge) {s, 0, -cost, a[s].size() - 1}); } int main() { read(n), read(m); tot = 0; for (int i = 1; i <= n; i++) { inp[i] = ++tot; outp[i] = ++tot; } s = inp[1], t = outp[n]; for (int i = 1; i <= n; i++) { if (i == 1 || i == n) addedge(inp[i], outp[i], INF, 0); else addedge(inp[i], outp[i], 1, 0); } for (int i = 1; i <= m; i++) { int x, y, z; read(x), read(y), read(z); addedge(outp[x], inp[y], 1, z); } for (int i = 1; i <= tot; i++) dist[i] = INF; while (spfa()) flow_path(); cout << flow << ' ' << cost << endl; return 0; }