HDU3594 Cactus ([good title] strong Connectivity Cactus diagram)

Test instructions: Judging is not the definition of Cactus diagram, Cactus diagram,
1. First of all, strong connectivity
2. Any of the times can only belong to a circle.
Analysis of cactus graphs

#include <cstdio>#include <iostream>#include <algorithm>#include <cmath>#include <set>#include <map>#include <string>#include <cstring>#include <stack>#include <queue>#include <vector>#include <cstdlib>#define Lson (rt<<1), L,m#define Rson (rt<<1|1), M+1,r#define M ((l+r) >>1)#define CL (A, B) memset (A,b,sizeof (a));#define LL Long Long#define P pair<int,int>#define X First#define Y Second#define PB Push_back#define FREAD (ZCC) freopen (ZCC, "R", stdin)#define FWRITE (ZCC) freopen (ZCC, "w", stdout)using namespace STD;Const intmaxn=20005;Const intinf=999999; vector<int>G[MAXN];intLOW[MAXN],DFN[MAXN],S[MAXN],BELONG[MAXN];BOOLINS[MAXN];intNum,cnt,top;BOOLOkBOOLVIS[MAXN];voidDfsintu) {low[u]=dfn[u]=++num; ins[u]=true; S[top++]=u;intN=g[u].size ();intsum=0; for(intI=0; i<n;i++) {intV=g[u][i];if(Vis[v]) ok=false;//Nature 1        if(!dfn[v]) {DFS (v);if(Low[v]>dfn[u]) ok=false;//Nature 2            if(Low[v]<dfn[u]) sum++;if(sum==2) ok=false;        Low[u]=min (Low[u],low[v]); }Else if(Ins[v])            {low[u]=min (dfn[v],low[u]); sum++;if(sum==2) ok=false;//Nature 3}    }if(Low[u]==dfn[u]) {intv=-1; cnt++; while(U!=V)            {V=s[--top]; ins[v]=false;        belong[v]=cnt; }} vis[u]=true;}voidTarjan (intN) {cl (DFN,0); CL (INS,false); CL (Belong,0); CL (VIS,false); ok=true; Num=top=cnt=0; for(intI=1; i<=n;i++) {if(!dfn[i]) DFS (i); }}intMain () {intTscanf("%d", &t); while(t--) {intNscanf("%d", &n); for(intI=0; i<=n;i++) {g[i].clear (); }intx, y; while(scanf("%d%d", &x,&y) && (x+y)) {x++;y++;        G[X].PB (y); } Tarjan (n);printf("%s\n", cnt==1&&ok?"YES":"NO"); }return 0;}

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HDU3594 Cactus ([good title] strong Connectivity Cactus diagram)