"K Short Circuit &a* algorithm" BZOJ1975: [Sdoi2010] Academy of Magical Pigs

Description find out the length of the 1~k short circuit. Solution

A * algorithm is used to solve the K short circuit

heuristic function of A * algorithm f (n) =g (n) +h (n)

g (n) is the actual cost of searching N in the state space

H (N) is the estimated cost of the best path from N to the end state

With respect to the selection of H (n), when H (n) < actual cost, the search is slow but solvable; h (n) = The actual cost, the correct rate and efficiency is the highest, h (n) > The actual cost, fast but only approximate solution can be obtained.

However, in the K short circuit problem, h (n) can be selected to the exact value, that is, N to the end of the node's shortest path, preprocessing from the end node to do once single source the shortest possible.

Expand the node in a wide-search manner, giving priority to the smallest node of f (n) at a time.

The second extension to the target node, the representative found a short circuit.

Correctness is well understood.

K Short Circuit about a * part of the code is very concise, with priority queue maintenance.

This problem is a naked problem, but this problem is very sick to let proirity_queuemle, so to handwritten heap.

Let me have this little handwritten STL dog QWQ.

Code

1#include <cstdio>2#include <algorithm>3#include <queue>4#include <cstring>5 using namespacestd;6 Const intn=5e3+5, m=2e5+5;7 8 DoubleD[n];9 inthead[n],e[m],nxt[m],cnt;Ten DoubleW[m]; One intAdde (intUintVDoubleg) { Ae[++cnt]=v;w[cnt]=g;nxt[cnt]=head[u];head[u]=CNT; - } - int_head[n],_e[m],_nxt[m],_cnt; the Double_w[m]; - int_adde (intUintVDoubleg) { -_e[++_cnt]=v;_w[_cnt]=g;_nxt[_cnt]=_head[u];_head[u]=_cnt; - } + structnode{ -     Doublef,g; +     into; A     BOOL operator< (Constnode&a) at         Const{returnf<A.F;} - }; - intn,m; - DoubleC; -  -queue<int>Q; in intInque[n]; - intSPFA () { tomemset (D,127,sizeof(d)); +d[n]=0; -inque[n]=1; the Q.push (n); *      $      while(!Q.empty ()) {Panax Notoginseng         intu=Q.front (); Q.pop (); -          for(intI=_head[u];i;i=_nxt[i]) { the             intv=_e[i]; +             if(d[v]>d[u]+_w[i]) { Ad[v]=d[u]+_w[i]; the                 if(!Inque[v]) { + Q.push (v); -inque[v]=1; $                 } $             } -         } -inque[u]=0; the     } - }Wuyi  the intans,size; -Node q[2000000]; Wu intPush (node x) { -     intNow,next; Aboutq[++size]=x; $now=size; -      while(now>1){ -Next=now>>1; -         if(Q[next]<q[now]) Break; A swap (Q[now],q[next]); +now=Next; the     } - } $ node Pop () { the     intNow,next; the node ret; theret=q[1]; theq[1]=q[size--]; -now=1; in      while((now<<1) <=size) { thenext=now<<1; the         if(next<size&&q[next+1]<q[next]) next++; About         if(Q[now]<q[next]) Break; the swap (Q[now],q[next]); thenow=Next; the     } +     returnret; - } the voidAstar () {BayiPush (node) {d[1],0,1}); the      while(size) { theNode x=pop (); -          for(intI=head[x.o];i;i=Nxt[i]) { -             intv=E[i]; thePush (node) {x.g+w[i]+d[v],x.g+w[i],v}); the         } the         if(x.o==N) { thec-=x.f; -             if(c<0)return; theans++; the         } the     }94 } the  the intMain () { thescanf"%D%D%LF",&n,&m,&c);98     intU,v;DoubleG; About      for(intI=1; i<=m;i++){ -scanf"%D%D%LF",&u,&v,&g);101 Adde (u,v,g);102 _adde (v,u,g);103     }104      the SPFA ();106 Astar ();107     108printf"%d\n", ans);109     return 0; the}

"K Short Circuit &a* algorithm" BZOJ1975: [Sdoi2010] Academy of Magical Pigs