ISAP模板

网络流问题 ISAP邻接表形式

const int MAXN = 100010; //点数的最大值
const int MAXM = 400010; //边数的最大值
const int INF = 0x3f3f3f3f;
struct Edge {
  int to, next, cap, flow;
} edge[MAXM]; //注意是MAXM
int tol;
int head[MAXN];
int gap[MAXN], dep[MAXN], pre[MAXN], cur[MAXN];
void init() {
  tol = 0;
  memset(head, -1, sizeof(head));
}

//加边，单向图三个参数，双向图四个参数
void addedge(int u, int v, int w, int rw = 0) {
  edge[tol].to = v;
  edge[tol].cap = w;
  edge[tol].next = head[u];
  edge[tol].flow = 0;
  head[u] = tol++;
  edge[tol].to = u;
  edge[tol].cap = rw;
  edge[tol].next = head[v];
  edge[tol].flow = 0;
  head[v] = tol++;
}
//输入参数：起点、终点、点的总数
//点的编号没有影响，只要输入点的总数
int sap(int start, int end, int N) {
  memset(gap, 0, sizeof(gap));
  memset(dep, 0, sizeof(dep));
  memcpy(cur, head, sizeof(head));
  int u = start;
  pre[u] = -1;
  gap[0] = N;
  int ans = 0;
  while (dep[start] < N) {
    if (u == end) {
      int Min = INF;
      for (int i = pre[u]; i != -1; i = pre[edge[i ^ 1].to])
        if (Min > edge[i].cap - edge[i].flow)
          Min = edge[i].cap - edge[i].flow;
      for (int i = pre[u]; i != -1; i = pre[edge[i ^ 1].to]) {
        edge[i].flow += Min;
        edge[i ^ 1].flow -= Min;
      }
      u = start;
      ans += Min;
      continue;
    }
    bool flag = false;
    int v;
    for (int 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] = pre[v] = i;
        break;
      }
    }
    if (flag) {
      u = v;
      continue;
    }
    int Min = N;
    for (int 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]])
      return ans;
    dep[u] = Min + 1;
    gap[dep[u]]++;
    if (u != start)
      u = edge[pre[u] ^ 1].to;
  }
  return ans;
}