最大流isap模板

  1 const int MAXN = 100010;
  2 const int MAXM = 400010;
  3 const int INF = 0x3f3f3f3f;
  4 struct Edge 
  5 {
  6     int to, next, cap, flow;
  7 }edge[MAXM];
  8 int tol;
  9 int head[MAXN];
 10 int gap[MAXN], dep[MAXN], cur[MAXN];
 11 void init() 
 12 {
 13     tol = 0;
 14     memset(head, -1, sizeof(head));
 15 }
 16 void addedge(int u, int v, int w, int rw = 0) 
 17 {
 18     edge[tol].to = v; edge[tol].cap = w; edge[tol].flow = 0;
 19     edge[tol].next = head[u]; head[u] = tol++;
 20     edge[tol].to = u; edge[tol].cap = rw; edge[tol].flow = 0;
 21     edge[tol].next = head[v]; head[v] = tol++;
 22 }
 23 int Q[MAXN];
 24 void BFS(int start, int end) 
 25 {
 26     memset(dep, -1, sizeof(dep));
 27     memset(gap, 0, sizeof(gap));
 28     gap[0] = 1;
 29     int front = 0, rear = 0;
 30     dep[end] = 0;
 31     Q[rear++] = end;
 32     while(front != end) {
 33         int u = Q[front++];
 34         for(int i = head[u]; i != -1; i = edge[i].next) {
 35             int v = edge[i].to;
 36             if(dep[v] != -1) continue;
 37             Q[rear++] = v;
 38             dep[v] = dep[u] + 1;
 39             gap[dep[v]]++;
 40         }
 41     }
 42 }
 43 int S[MAXN];
 44 int sap(int start, int end, int N) {  //start是源点编号，end是汇点编号，N是点的总数，返回最大流
 45     BFS(start, end);
 46     memcpy(cur, head, sizeof(head));
 47     int top = 0;
 48     int u = start;
 49     int ans = 0;
 50     while(dep[start] < N) 
 51     {
 52         if(u == end) 
 53         {
 54             int Min = INF;
 55             int inser;
 56             for(int i = 0; i < top; i++)
 57                 if(Min > edge[S[i]].cap - edge[S[i]].flow) {
 58                     Min = edge[S[i]].cap - edge[S[i]].flow;
 59                     inser = i;
 60                 }
 61             for(int i = 0; i < top; i++) 
 62             {
 63                 edge[S[i]].flow += Min;
 64                 edge[S[i]^1].flow -= Min;
 65             }
 66             ans += Min;
 67             top = inser;
 68             u = edge[S[top]^1].to;
 69             continue;
 70         }
 71         bool flag = false;
 72         int v;
 73         for(int i = cur[u]; i != -1; i = edge[i].next) 
 74         {
 75             v = edge[i].to;
 76             if(edge[i].cap - edge[i].flow && dep[v] + 1 == dep[u])                          
 77                 flag = true;
 78                 cur[u] = i;
 79                 break;
 80             }
 81         }
 82         if(flag) 
 83         {
 84             S[top++] = cur[u];
 85             u = v;
 86             continue;
 87         }
 88         int Min = N;
 89         for(int i = head[u]; i != -1; i = edge[i].next)
 90             if(edge[i].cap - edge[i].flow && dep[edge[i].to] < Min) 
 91             {
 92                 Min = dep[edge[i].to];
 93                 cur[u] = i;
 94             }
 95         gap[dep[u]]--;
 96         if(!gap[dep[u]]) return ans;
 97         dep[u] = Min + 1;
 98         gap[dep[u]]++;
 99         if(u != start) u = edge[S[--top]^1].to;
100     }
101     return ans;
102 }