ISAP（gap优化+当前弧优化+非递归）.cpp

#include <bits/stdc++.h>
using namespace std;
namespace ISAP {

//邻接表形式+手动栈（非递归）
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, head[MAXN];
int gap[MAXN], dep[MAXN], cur[MAXN];
void init() {
    tol = 0;
    memset(head, -1, sizeof(head));
}
void addedge(int u, int v, int w, int rw = 0) {
    edge[tol].to = v;
    edge[tol].cap = w;
    edge[tol].flow = 0;
    edge[tol].next = head[u];
    head[u] = tol++;
    edge[tol].to = u;
    edge[tol].cap = rw;
    edge[tol].flow = 0;
    edge[tol].next = head[v];
    head[v] = tol++;
}
int Q[MAXN];
void BFS(int st, int ed) {
    memset(dep, -1, sizeof(dep));
    memset(gap, 0, sizeof(gap));
    gap[0] = 1;
    int frt = 0, rear = 0;
    dep[ed] = 0;
    Q[rear++] = ed;
    while(frt != rear) {
        int u = Q[frt++];
        for(int i = head[u]; i != -1; i = edge[i].next) {
            int 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 st, int ed, int N) {
    BFS(st, ed);
    memcpy(cur, head, sizeof(head));
    int top = 0;
    int u = st;
    int ans = 0;
    while(dep[st] < N) {
        if(u == ed) {
            int Min = INF;
            int inser;
            for(int i = 0; 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 = 0; i < top; i++) {
                edge[S[i]].flow += Min;
                edge[S[i] ^ 1].flow -= Min;
            }
            ans += Min;
            top = inser;
            u = edge[S[top] ^ 1].to;
            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] = i;
                break;
            }
        }
        if(flag) {
            S[top++] = cur[u];
            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 != st) u = edge[S[--top] ^ 1].to;
    }
    return ans;
}
}

int main(int argc, char **argv) {

    return 0;
}