Topological sorting, tree's diameter template (cf14d enum-delete edge)

The diameter of the HDU4607 tree

#include <stdio.h>#include <string.h>#include <iostream>#include <queue>#include <vector>using namespace STD;#define N 100005#define INF 1<<30intN,dis[n],e;BOOLVis[n]; vector<int>G[n];//Note that the marking is starting at 0 or 1intBFS (intx) {intI for(i=0; i<=n;i++) Dis[i]=inf;memset(Vis,0,sizeof(VIS)); Queue<int>Q while(!q.empty ()) Q.pop ();    Q.push (x); dis[x]=0; while(!q.empty ()) {intU=q.front (); Q.pop (); vis[u]=1; for(i=0; I<g[u].size (); i++) {intV=g[u][i];if(dis[v]>dis[u]+1) {dis[v]=dis[u]+1; E=v;if(!vis[v]) {vis[v]=1; Q.push (v); }            }        }    }returnE;}intMain () {intT,i,que;scanf("%d", &t); while(t--) {scanf("%d%d", &n,&que); for(i=0; i<=n;i++) g[i].clear (); for(i=1; i<n;i++) {intb;scanf("%d%d", &a,&b);            G[a].push_back (b);        G[b].push_back (a); } E=BFS (1); E=BFS (E); while(que--) {intUscanf("%d", &u);if(u<=dis[e]+1)printf("%d\n", U-1);Else printf("%d\n", dis[e]+ (U-dis[e]+1))*2);//If the crossing node is greater than the point on the tree diameter, go to the loop (obviously the loop is the part that walks the branch, RT) diameter + loop}    }return 0;}

Codeforces 14D diameter of Paths tree

Test instructions: Given a tree
Find 2-point non-repeating path, so that the length of the two paths is the largest product
Ideas:
1, in order to ensure that the point does not repeat, in the picture to delete an edge, enumerate the deletion of the edge
2, so get 2 trees, in their own tree to find the longest chain, that is, the diameter of the tree, and then multiply it

#include <stdio.h>#include <iostream>#include <string.h>#include <set>#include <vector>#include <map>#include <math.h>#include <queue>#include <string>#include <stdlib.h>#include <algorithm>using namespace STD;#define NstructEdge {intFrom, to, NEX;BOOLhehe;} edge[n<<1];intHead[n], Edgenum;voidAddintUintV) {Edge e={u,v,head[u],true};    Edge[edgenum] = E; Head[u] = Edgenum + +;}intNintDis[n];voidInit () {memset(Head,-1,sizeofHead); Edgenum =0; }intBFsintx) {memset(Dis,0,sizeofDIS); DIS[X] =1; Queue<int>Q Q.push (x);inthehe = x; while(!q.empty ()) {intU = Q.front (); Q.pop (); for(inti = Head[u]; ~i; i = Edge[i].nex) {if(!edge[i].hehe)Continue;intv = edge[i].to;if(Dis[v])Continue; DIS[V] = dis[u]+1, Q.push (v);if(Dis[hehe]<dis[v]) hehe = v; }    }returnhehe;}intMain () {intI, u, v; while(~scanf("%d", &n)) {init (); for(i=1; i<n;i++) {scanf("%d%d", &u,&v); Add (U,V);        Add (V,u); }intAns =0; for(i =0; i < Edgenum; i+=2) {Edge[i].hehe = edge[i^1].hehe =false; u = edge[i].from; v = edge[i].to;intL1 = BFS (u);intR1 = BFS (L1);intMUL1 = Dis[r1]-1;intL2 = BFS (v);intR2 = BFS (L2);intMUL2 = Dis[r2]-1;            ans = max (ans, mul1 * mul2); Edge[i].hehe = edge[i^1].hehe =true; }printf("%d\n", ans); }return 0;}

Topological sorting

#include <cstdio>#include <cstring>#include <iostream>#include <algorithm>#include <queue>using namespace STD;Const intmaxn= -;intEXGCD (intAintBint&x,int&y) {if(b==0) {x =1; y =0;returnA }intR = EXGCD (b,a%b,x,y);intt = x;    x = y; y = t-a/b*y;returnR;}intHEAD[MAXN],IP,INDEGREE[MAXN];intN,M,SEQ[MAXN];structnote{intV,next;} EDGE[MAXN*MAXN];voidInit () {memset(head,-1,sizeof(head)); ip=0;}voidAddedge (intUintV) {edge[ip].v=v,edge[ip].next=head[u],head[u]=ip++;}intTopo ()/// topology, template can be made{ Queue<int>QintINDEG[MAXN]; for(intI=0; i<n; i++) {Indeg[i]=indegree[i];if(indeg[i]==0) Q.push (i); }intk=0;BOOLres=false; while(!q.empty ()) {if(Q.size ()! =1) res=true;intU=q.front ();        Q.pop (); Seq[k++]=u; for(intI=head[u]; i!=-1; I=edge[i].next) {intV=EDGE[I].V; indeg[v]--;if(indeg[v]==0) Q.push (v); }    }if(k<n)return-1;///There is a forward loop, in short, topological ordering is not possible    if(RES)return 0;//// can be topological ordered, and only one way, seq array is a well-ordered sequence    return 1;/// can be topological ordered, there are many cases, SEQ array is one of the sequence}intMain () {intx, y;intR = EXGCD ( at,5, x, y); R = EXGCD ( at,5, x, y);printf(" %d%d%d", r,x,y);return 0;}

Topological sorting, tree's diameter template (cf14d enum-delete edge)