ISAP

Posted 2021-01-23 cgjh

struct Edge {
    int lst;
    int v;
    int w;
};

const int maxn = 1e5+500;
const int maxe = (1e5+500) * 2;
const int  inf = 0x3f3f3f3f;

class ISAP {
public :
    Edge edge[maxe];
    int head[maxn], qsz;
    int d[maxn], cur[maxn], num[maxn];
    int st, ed, n;

    void add(int u, int v, int w) {
        edge[qsz] = (Edge){head[u], v, w};
        head[u] = qsz++;
        edge[qsz] = (Edge){head[v], u, w};
        head[v] = qsz++;
    }

    void bfs(int t) {
        queue<int> q;
        memset(num, 0, sizeof(num));
        memset(d,   0, sizeof(d));
        for (int i=1; i<=n; ++i) cur[i] = head[i];
        d[t] = 1;
        num[d[t]]++;
        q.push(t);
        while (!q.empty()) {
            int u = q.front(); q.pop();
            for (int i=head[u]; ~i; i=edge[i].lst) {
                int v = edge[i].v;
                if (!d[v]) {
                    d[v] = d[u] + 1;
                    num[d[v]]++;
                    q.push(v);
                }
            }
        }
    }

    int dfs(int u, int limit) {
        if (u==ed) return limit;
        int flow = 0, v;
        for (int i=cur[u]; ~i; i=cur[u]=edge[i].lst) {
            v = edge[i].v;
            if (d[u] == d[v] + 1) {
                int f = dfs(v, min(limit, edge[i].w));
                flow += f;
                limit -= f;
                edge[i].w -= f;
                edge[i^1].w += f;
                if (!limit) return flow;
            }
        }
        if (!(--num[d[u]])) d[st] = n + 1;
        d[u] += 1;
        ++num[d[u]];
        cur[u] = head[u];
        return flow;
    }

    void init(int n) {
        this->n = n;
        qsz = 0;
        memset(head, -1, sizeof head);
    }

    int maxflow(int st, int ed) {
        bfs(ed);
        this->st = st; this->ed = ed;
        int res = 0;
        do {
            res += dfs(st, inf);
        } while (d[st] <= n);
        return res;
    }
}isap;