[HDOJ5889]Barricade（spfa，最大流）

Posted 2020-08-09

题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=5889

求出所有最短路，标记好以后跑最大流就是最小割。

  1 #include <bits/stdc++.h>
  2 using namespace std;
  3 #define fr first
  4 #define sc second
  5 #define cl clear
  6 #define BUG puts("here!!!")
  7 #define W(a) while(a--)
  8 #define pb(a) push_back(a)
  9 #define Rint(a) scanf("%d", &a)
 10 #define Rll(a) scanf("%lld", &a)
 11 #define Rs(a) scanf("%s", a)
 12 #define Cin(a) cin >> a
 13 #define FRead() freopen("in", "r", stdin)
 14 #define FWrite() freopen("out", "w", stdout)
 15 #define Rep(i, len) for(int i = 0; i < (len); i++)
 16 #define For(i, a, len) for(int i = (a); i < (len); i++)
 17 #define Cls(a) memset((a), 0, sizeof(a))
 18 #define Clr(a, x) memset((a), (x), sizeof(a))
 19 #define Full(a) memset((a), 0x7f7f7f, sizeof(a))
 20 #define lrt rt << 1
 21 #define rrt rt << 1 | 1
 22 #define pi 3.14159265359
 23 #define RT return
 24 #define lowbit(x) x & (-x)
 25 #define onenum(x) __builtin_popcount(x)
 26 typedef long long LL;
 27 typedef long double LD;
 28 typedef unsigned long long ULL;
 29 typedef pair<int, int> pii;
 30 typedef pair<string, int> psi;
 31 typedef pair<LL, LL> pll;
 32 typedef map<string, int> msi;
 33 typedef vector<int> vi;
 34 typedef vector<LL> vl;
 35 typedef vector<vl> vvl;
 36 typedef vector<bool> vb;
 37 
 38 const int maxn = 1100;
 39 const int maxm = 11000;
 40 const int inf = 1000000000;
 41 typedef struct Edge {
 42   int u, v, w;
 43   int next;
 44   Edge() { next = -1; }
 45 }Edge;
 46 
 47 int n, m, s, t;
 48 Edge edge[maxm];
 49 int head[maxn], ecnt;
 50 int d[maxn];
 51 bool vis[maxn];
 52 int u, v, w;
 53 
 54 int cnt, dhead[maxn];
 55 int cur[maxn], dd[maxn];
 56 Edge dedge[maxm];
 57 int S, T, N;
 58 
 59 void adde(int u, int v, int w) {
 60   edge[ecnt].u = u; edge[ecnt].v = v; edge[ecnt].w = w;
 61   edge[ecnt].next = head[u]; head[u] = ecnt++;
 62 }
 63 
 64 void init() {
 65   Clr(head, -1); ecnt = 0; Cls(vis);
 66   Cls(edge);
 67   Clr(dhead, -1); Cls(dedge);
 68     cnt = 0;
 69 }
 70 
 71 void spfa(int s) {
 72   queue<int> q;
 73   Rep(i, n+1) d[i] = inf;
 74   d[s] = 0; q.push(s);
 75   vis[s] = 1;
 76   while(!q.empty()) {
 77     int u = q.front(); q.pop(); vis[u] = 0;
 78     for(int i = head[u]; ~i; i=edge[i].next) {
 79       int v = edge[i].v;
 80       if(d[v] > d[u] + 1) {
 81         d[v] = d[u] + 1;
 82         if(!vis[v]) {
 83           vis[v] = 1;
 84           q.push(v);
 85         }
 86       }
 87     }
 88   }
 89 }
 90 
 91 void dadde(int u, int v, int w, int c1) {
 92     dedge[cnt].u = u; dedge[cnt].v = v; dedge[cnt].w = w;
 93     dedge[cnt].next = dhead[u]; dhead[u] = cnt++;
 94     dedge[cnt].u = v; dedge[cnt].v = u; dedge[cnt].w = c1;
 95     dedge[cnt].next = dhead[v]; dhead[v] = cnt++;
 96 }
 97 
 98 bool bfs(int s, int t, int n) {
 99     queue<int> q;
100     for(int i = 0; i < n; i++) dd[i] = inf;
101     dd[s] = 0;
102     q.push(s);
103     while(!q.empty()) {
104         int u = q.front(); q.pop();
105         for(int i = dhead[u]; ~i; i = dedge[i].next) {
106             if(dd[dedge[i].v] > dd[u] + 1 && dedge[i].w > 0) {
107                 dd[dedge[i].v] = dd[u] + 1;
108                 if(dedge[i].v == t) return 1;
109                 q.push(dedge[i].v);
110             }
111         }
112     }
113     return 0;
114 }
115 
116 int dinic(int s, int t, int n) {
117     int st[maxn], top;
118     int u;
119     int flow = 0;
120     while(bfs(s, t, n)) {
121         for(int i = 0; i < n; i++) cur[i] = dhead[i];
122         u = s; top = 0;
123         while(cur[s] != -1) {
124             if(u == t) {
125                 int tp = inf;
126                 for(int i = top - 1; i >= 0; i--) {
127                     tp = min(tp, dedge[st[i]].w);
128                 }
129                 flow += tp;
130                 for(int i = top - 1; i >= 0; i--) {
131                     dedge[st[i]].w -= tp;
132                     dedge[st[i] ^ 1].w += tp;
133                     if(dedge[st[i]].w == 0) top = i;
134                 }
135                 u = dedge[st[top]].u;
136             }
137             else if(cur[u] != -1 && dedge[cur[u]].w > 0 && dd[u] + 1 == dd[dedge[cur[u]].v]) {
138                 st[top++] = cur[u];
139                 u = dedge[cur[u]].v;
140             }
141             else {
142                 while(u != s && cur[u] == -1) {
143                     u = dedge[st[--top]].u;
144                 }
145                 cur[u] = dedge[cur[u]].next;
146             }
147         }
148     }
149     return flow;
150 }
151 
152 signed main() {
153   //FRead();
154   int ttt;
155   Rint(ttt);
156   W(ttt) {
157     init();
158     Rint(n); Rint(m);
159     Rep(i, m) {
160       Rint(u); Rint(v); Rint(w);
161       adde(u,v,w); adde(v,u,w);
162     }
163     spfa(1);
164     Rep(i, ecmt) {
165       if(d[edge[i].v] == d[edge[i].u] + 1) {
166         dadde(edge[i].u-1, edge[i].v-1, edge[i].w, 0);
167       }
168     }
169     S = 0; T = n - 1; N = n;
170     printf("%d\n", dinic(S, T, N));
171   }
172   RT 0;
173 }