最大流isap模板

isap+bfs初始化+栈优化，点的编号从0开始：

 const int MAXN = ;
 const int MAXM = ;
 const int INF = 0x3f3f3f3f;
 struct Edge
 {
     int to, next, cap, flow;
 }edge[MAXM];
 int tol;
 int head[MAXN];
 int gap[MAXN], dep[MAXN], cur[MAXN];
 void init()
 {
     tol = ;
     memset(head, -, sizeof(head));
 }
 void addedge(int u, int v, int w, int rw = )
 {
     edge[tol].to = v; edge[tol].cap = w; edge[tol].flow = ;
     edge[tol].next = head[u]; head[u] = tol++;
     edge[tol].to = u; edge[tol].cap = rw; edge[tol].flow = ;
     edge[tol].next = head[v]; head[v] = tol++;
 }
 int Q[MAXN];
 void BFS(int start, int end)
 {
     memset(dep, -, sizeof(dep));
     memset(gap, , sizeof(gap));
     gap[] = ;
     int front = , rear = ;
     dep[end] = ;
     Q[rear++] = end;
     while(front != end) {
         int u = Q[front++];
         for(int i = head[u]; i != -; i = edge[i].next) {
             int v = edge[i].to;
             if(dep[v] != -) continue;
             Q[rear++] = v;
             dep[v] = dep[u] + ;
             gap[dep[v]]++;
         }
     }
 }
 int S[MAXN];
 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
     BFS(start, end);
     memcpy(cur, head, sizeof(head));
     int top = ;
     int u = start;
     int ans = ;
     while(dep[start] < N)
     {
         if(u == end)
         {
             int Min = INF;
             int inser;
             for(int i = ; i < top; i++)
                 if(Min > edge[S[i]].cap - edge[S[i]].flow) {
                     Min = edge[S[i]].cap - edge[S[i]].flow;
                     inser = i;
                 }
             for(int i = ; i < top; i++)
             {
                 edge[S[i]].flow += Min;
                 edge[S[i]^].flow -= Min;
             }
             ans += Min;
             top = inser;
             u = edge[S[top]^].to;
             continue;
         }
         bool flag = false;
         int v;
         for(int i = cur[u]; i != -; i = edge[i].next)
         {
             v = edge[i].to;
             if(edge[i].cap - edge[i].flow && dep[v] +  == dep[u])
                 flag = true;
                 cur[u] = i;
                 break;
             }
         }
         if(flag)
         {
             S[top++] = cur[u];
             u = v;
             continue;
         }
         int Min = N;
         for(int i = head[u]; i != -; i = edge[i].next)
             if(edge[i].cap - edge[i].flow && dep[edge[i].to] < Min)
             {
                 Min = dep[edge[i].to];
                 cur[u] = i;
             }
         gap[dep[u]]--;
         if(!gap[dep[u]]) return ans;
         dep[u] = Min + ;
         gap[dep[u]]++;
         if(u != start) u = edge[S[--top]^].to;
     }
     return ans;
 }