最大流 ISAP

const int MAXN = 2010;//点数const int MAXM = 400010;//正向弧和反向弧的数量#######################################################################################################################################struct Edge{    int to,next,cap,flow;} edge[MAXM];int Top;int head[MAXN];int gap[MAXN],dep[MAXN],cur[MAXN];void Init(){    Top = 0;    memset(head,-1,sizeof(head));}void Link(int u,int v,int w){    edge[Top].to = v,edge[Top].cap = w,edge[Top].flow = 0;    edge[Top].next = head[u],head[u] = Top++;    edge[Top].to = u,edge[Top].cap = 0,edge[Top].flow = 0;    edge[Top].next = head[v],head[v] = Top++;}int Q[MAXN];void BFS(int S,int E){    memset(dep,-1,sizeof(dep));    memset(gap,0,sizeof(gap));    int u,v,i,Front = 0,Rear = 0;    dep[E] = 0;    Q[Rear++] = E;    gap[0] = 1;    while(Front != Rear)    {        u = Q[Front++];        for(i = head[u]; i != -1; i = edge[i].next)        {            v = edge[i].to;            if(dep[v] != -1) continue;            Q[Rear++] = v;            dep[v] = dep[u] + 1;            gap[dep[v]]++;        }    }}int S[MAXN];int ISAP(int Start,int End,int N){    BFS(Start,End);    if(dep[Start] == -1)        return 0;    memcpy(cur,head,sizeof(head));    int Top = 0;    int u = Start,v;    int flow = 0;    int Min;    int inser;    int i;    while(dep[Start] < N)    {        if(u == End){            Min = INF,inser = -1;            for(i = 0;i < Top; ++i)                if(Min > edge[S[i]].cap - edge[S[i]].flow)                    inser = i,Min = edge[S[i]].cap - edge[S[i]].flow;            for(i = 0 ; i < Top; ++i)                edge[S[i]].flow += Min,edge[S[i]^1].flow -= Min;            flow += Min;            Top = inser;            u = edge[S[Top]^1].to;            continue;        }        bool flag = false;        for(i =  cur[u];i != -1 ;i = edge[i].next)        {            v = edge[i].to;            if(edge[i].cap-edge[i].flow && dep[v] + 1  == dep[u]){                flag = true;                cur[u] = i;                break;            }        }        if(flag){            S[Top++] = cur[u];            u = v;            continue;        }        int Min = N;        for(i = head[u] ; i != -1;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]] == 0)            return flow;        dep[u] = Min+1;        gap[dep[u]]++;        if(u != Start) u = edge[S[--Top]^1].to;    }    return flow;}