【BZOJ1570】[JSOI2008]Blue Mary的旅行【最大流】

【题目链接】

太神啦。【POPOQQQ的题解】

/* Telekinetic Forest Guard */#include <cstdio>#include <cstring>#include <algorithm>using namespace std;const int maxn = 6005, maxm = 300005, maxe = 2505, maxq = 10000, inf = 0x3f3f3f3f;int n, m, k, head[maxn], cur[maxn], cnt, tot, bg, ed, depth[maxn], q[maxq];struct _edge {int v, w, next;} g[maxm << 1];struct _data {int u, v, w;} e[maxe];inline int iread() {int f = 1, x = 0; char ch = getchar();for(; ch < '0' || ch > '9'; ch = getchar()) f = ch == '-' ? -1 : 1;for(; ch >= '0' && ch <= '9'; ch = getchar()) x = x * 10 + ch - '0';return f * x;}inline void add(int u, int v, int w) {g[cnt] = (_edge){v, w, head[u]};head[u] = cnt++;}inline void insert(int u, int v, int w) {add(u, v, w); add(v, u, 0);}inline bool bfs() {for(int i = 0; i <= tot; i++) depth[i] = -1; depth[ed] = -1;int h = 0, t = 0, u, i; depth[q[t++] = bg] = 0;while(h != t) for(i = head[u = q[h++]]; ~i; i = g[i].next) if(g[i].w && !~depth[g[i].v]) {depth[g[i].v] = depth[u] + 1;if(g[i].v == ed) return 1;q[t++] = g[i].v;}return 0;}inline int dfs(int x, int flow) {if(x == ed) return flow;int left = flow;for(int i = cur[x]; ~i; i = g[i].next) if(g[i].w && depth[g[i].v] == depth[x] + 1) {int tmp = dfs(g[i].v, min(g[i].w, left));left -= tmp; g[i].w -= tmp; g[i ^ 1].w += tmp;if(g[i].w) cur[x] = i;if(!left) return flow;}if(left == flow) depth[x] = -1;return flow - left;}int main() {n = iread(); m = iread(); k = iread();for(int i = 1; i <= m; i++) e[i].u = iread(), e[i].v = iread(), e[i].w = iread();for(int i = 0; i < maxn; i++) head[i] = -1; cnt = 0;bg = 0; ed = maxn - 1;int ans = 0;insert(bg, 1, k);for(int i = 1; i <= n + k; i++) {for(int j = 1; j <= m; j++) insert((i - 1) * n + e[j].u, i * n + e[j].v, e[j].w);for(int j = 1; j <= n; j++) insert((i - 1) * n + j, i * n + j, inf);insert(i * n + n, ed, inf);tot = i * n + n;while(bfs()) {for(int i = 0; i <= tot; i++) cur[i] = head[i]; cur[ed] = head[ed];ans += dfs(bg, inf);}if(ans == k) {printf("%d\n", i);break;}}return 0;}