震惊！全机房一半的ISAP竟然都挂了

今天写CF311E Biologist的时候忽然发现自己的ISAP一直跑不出一张图

然后一直调试无果后怀疑自己的ISAP

然后调了调发现——ISAP挂了

数据如下（附图片）：

 1 1 -> 23324 [label = " 5 "]
 2 2 -> 23324 [label = " 10 "]
 3 23323 -> 3 [label = " 8 "]
 4 4 -> 23324 [label = " 5 "]
 5 23323 -> 5 [label = " 4 "]
 6 10012 -> 5 [label = " 1061109567 "]
 7 10012 -> 4 [label = " 1061109567 "]
 8 10012 -> 1 [label = " 1061109567 "]
 9 23323 -> 10012 [label = " 7 "]
10 10013 -> 1 [label = " 1061109567 "]
11 10013 -> 3 [label = " 1061109567 "]
12 10013 -> 5 [label = " 1061109567 "]
13 23323 -> 10013 [label = " 10 "]
14 2 -> 10014 [label = " 1061109567 "]
15 1 -> 10014 [label = " 1061109567 "]
16 4 -> 10014 [label = " 1061109567 "]
17 10014 -> 23324 [label = " 8 "]
18 10015 -> 5 [label = " 1061109567 "]
19 10015 -> 2 [label = " 1061109567 "]
20 10015 -> 3 [label = " 1061109567 "]
21 23323 -> 10015 [label = " 0 "]
22 10016 -> 2 [label = " 1061109567 "]
23 10016 -> 4 [label = " 1061109567 "]
24 10016 -> 5 [label = " 1061109567 "]
25 23323 -> 10016 [label = " 7 "]
26 //这个是给画图软件用的数据

然后发现不止我的ISAP，还有其他几位DL的似乎也挂了

用了半年的板子......

ISAP板子如下：

  1 struct Queue{
  2     int s, t;
  3     int q[MAXN];
  4     Queue(){s = 1, t = 0;}
  5     inline void clear(){
  6         s = 1, t = 0;
  7     }
  8     inline bool empty(){
  9         return s > t;
 10     }
 11     inline int size(){
 12         return t - s + 1;
 13     }
 14     inline void push(int tar){
 15         q[++ t] = tar;
 16     }
 17     inline int front(){
 18         return q[s];
 19     }
 20     inline void pop(){
 21         s ++;
 22     }
 23 };
 24 
 25 struct Graph{
 26     int tot;
 27     int beginx[MAXN], endx[MAXM], nxt[MAXM], res[MAXM];
 28     Graph(){
 29         tot = 1;
 30     }
 31     inline void Init(){
 32         tot = 1;
 33         memset(beginx, 0, sizeof(beginx));
 34     }
 35     inline void add_edge(int u, int v, int r){
 36         Debug(u, "->", v, "[label = \"", r, "\"]");//Debug...
 37         nxt[++ tot] = beginx[u], beginx[u] = tot, endx[tot] = v, res[tot] = r;
 38         nxt[++ tot] = beginx[v], beginx[v] = tot, endx[tot] = u, res[tot] = 0;
 39     }
 40 }ori;
 41 
 42 struct ISap{
 43     Graph g;
 44     Queue mession;
 45     int max_f, now_f, pt;
 46     int cur[MAXN], d[MAXN], num[MAXN], pre[MAXN];
 47     inline void BFS(){
 48         mession.clear();
 49         mession.push(t);
 50         memset(d, 0, sizeof(d));//注意加了边之后一定要更新
 51         memset(num, 0, sizeof(num));
 52         d[t] = 1;
 53         int u, v;
 54         while(!mession.empty()){
 55             u = mession.front();
 56             mession.pop();
 57             num[d[u]] ++;
 58             for(int i = g.beginx[u]; i; i = g.nxt[i]){
 59                 v = g.endx[i];
 60                 if(!d[v] && g.res[i ^ 1]){//...
 61                     d[v] = d[u] + 1;
 62                     mession.push(v);
 63                 }
 64             }
 65         }
 66     }
 67     inline void argu(){
 68         while(pt != s){
 69             g.res[pre[pt]] -= now_f, g.res[pre[pt] ^ 1] += now_f;
 70             pt = g.endx[pre[pt] ^ 1];
 71         }
 72         max_f += now_f;
 73     }
 74     inline int ISAP(){
 75         max_f = 0, now_f = INF, pt = s;
 76         BFS();
 77         memcpy(cur, g.beginx, sizeof(cur));//注意加了边之后一定要
 78         bool done;
 79         while(d[s] < MAXN - 5){
 80             if(pt == t) argu(), now_f = INF;//WTF??
 81             done = false;
 82             for(int &i = cur[pt]; i; i = g.nxt[i]){
 83                 int v = g.endx[i];
 84                 if(g.res[i] && d[v] == d[pt] - 1){
 85                     pre[v] = i;
 86                     pt = v;//...
 87                     done = true;
 88                     LKF::upmin(now_f, g.res[i]);
 89                     break;
 90                 }
 91             }
 92             if(!done){
 93                 int heig = MAXN - 4;
 94                 for(int i = g.beginx[pt]; i; i = g.nxt[i]){
 95                     int v = g.endx[i];
 96                     if(g.res[i]) LKF::upmin(heig, d[v] + 1);
 97                 }
 98                 if(-- num[d[pt]] == 0) return max_f;
 99                 cur[pt] = g.beginx[pt];
100                 num[d[pt] = heig] ++;
101                 if(pt != s) pt = g.endx[pre[pt] ^ 1];
102             }
103         }
104         return max_f;
105     }
106 }isap;

初步原因观察到的是：

1. now_f流量在回到了s之后没有被重置回INF
2. 分层图有问题，会导致提前退出算法

有关原因待分析