Spoj topic 375 Query on a tree (link cut tree edge Update, ask for two points maximum)

Qtree-query on a treeNo Tags

You were given a tree (an acyclic undirected connected graph) with N nodes, and edges numbered 1, 2, 3 ... N-1.

We'll ask you to perfrom some instructions of the following form:

• Change i ti : Change the cost of the i-th edge to Ti
  Or
• QUERY a B : Ask for the maximum edge cost on the path from Node A to Node B

Input

The first line of input contains an integer T, the number of test cases (T <= 20). T test cases follow.

For each test case:

• in the first line there was an Integer n   (n  <= 10000),
• in The Next n -1 lines, the i-th line describes the i-th edge:a line with three int Egers a b C  denotes an edge between  a , b  of cost c   (c  <= 1000000),
• The next lines contain Instructions  "change I ti"  or  "QUERY a B" ,
• the end of each test case was signified by the string "done ".

There is one blank line between successive tests.

Output

For each "QUERY" operation, the write one integer representing its result.

Example

Input:131 2 3 2QUERY 1 2CHANGE 1 3QUERY 1 2DONEOutput:1
3
#include <stdio.h> #include <string.h> #include <stdlib.h> #include <queue> #include <iostre  Am> #define MAX (A, B) (A&GT;B?A:B) using namespace std;  int head[50050],cnt,vis[50050];  struct S {int u,v,w,next;  }edge[50050<<1];      struct LCT {int bef[50050],pre[50050],next[50050][2],key[50050],val[50050],belong[50050];          void Init () {memset (pre,0,sizeof (pre));        memset (Next,0,sizeof (next));      } void Pushup (int x) {Val[x]=max (Key[x],max (val[next[x][1]],val[next[x][0]));            } void rotate (int x,int kind) {int y,z;            Y=PRE[X];            Z=pre[y];            Next[y][!kind]=next[x][kind];            Pre[next[x][kind]]=y;            Next[z][next[z][1]==y]=x;            Pre[x]=z;            Next[x][kind]=y;          Pre[y]=x;      Pushup (y);            } void Splay (int x) {int rt;      for (Rt=x;pre[rt];rt=pre[rt]);      if (X!=RT) {BEF[X]=BEF[RT];                bef[rt]=0; while (Pre[x]) {if (next[pre[x]][0]==x) {Rotat                    E (x,1);                } else rotate (x,0);          } pushup (x);            }} void access (int x) {int fa;                for (Fa=0;x;x=bef[x]) {splay (x);                pre[next[x][1]]=0;                Bef[next[x][1]]=x;                NEXT[X][1]=FA;                Pre[fa]=x;                bef[fa]=0;                Fa=x;          Pushup (x);          }} void Change (int x,int val) {int t;          T=BELONG[X-1];          Key[t]=val;      Splay (t);          } int query (int x,int y) {access (Y);              for (Y=0;x;x=bef[x]) {splay (x);                 if (!bef[x]) Return Max (val[y],val[next[x][1]);              pre[next[x][1]]=0;              Bef[next[x][1]]=x;              Next[x][1]=y;              Pre[y]=x;              bef[y]=0;              Y=x;          Pushup (x);  }}}LCT;      void Add (int u,int v,int W) {edge[cnt].u=u;      Edge[cnt].v=v;      Edge[cnt].w=w;      Edge[cnt].next=head[u];  head[u]=cnt++;      } void BFs (int u) {int i,y;      queue<int>q;      memset (vis,0,sizeof (VIS));      Vis[u]=1;      Q.push (U);          while (!q.empty ()) {U=q.front ();          Q.pop ();              for (int i=head[u];i!=-1;i=edge[i].next) {int v=edge[i].v;                  if (!vis[v]) {lct.bef[v]=u;                  LCT.KEY[V]=LCT.VAL[V]=EDGE[I].W;                  lct.belong[i>>1]=v;                  Vis[v]=1;              Q.push (v); }}}} int main () {int t;scanf ("%d", &t), while (t--) {int N;memset (head,-1,sizeof (head)); Cnt=0;int I;char s[10];scanf ("%d", &n); for (i=1;i<n;i++) {int a,b,c;scanf ("%d%d%d", &a,&b,&c); Add (a,b,c); add (b,a,c);} Lct.init (); BFS (1); while (scanf ("%s", s)!=eof) {int a,b;if (strcmp (S, "done") ==0) break;scanf ("%d%d", &a,&b); if (s[0]== ' Q ') {printf ("%d\n", Lct.query (A, b));} Elselct.change (A, b);}}}

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Spoj topic 375 Query on a tree (link cut tree edge Update, ask for two points maximum)