diameter and multiplication of URAL 1752 tree 2 Trees

Assume that the two endpoints of the tree's diameter are p0,p1. If a point q satisfies the requirement for a single query (v,k), then Q must be on the path from V to P0 or V to P1.

The rest is to look for p in the tree. Multiply it.

#include <algorithm> #include <iostream> #include <cstring> #include <cstdlib> #include < cstdio> #include <queue> #include <cmath> #include <stack> #include <map> #define LL long long# Define ULL unsigned long long#define INF 0x3f3f3f3fusing namespace std;const int maxn = 20010;const int MAXM = 15;struct N {int v,next;}    Edge[2*maxn];int head[maxn];int top;void Link (int u,int v) {edge[top].v = v;    Edge[top].next = Head[u]; Head[u] = top++;}    int pa[2][maxn][maxm];int dep[2][maxn];void INITDEPFA (int s,int lay,int pre = -1,int d = 0) {Dep[lay][s] = D;    Pa[lay][s][0] = pre; for (int p = head[s];p! =-1; p = edge[p].next) {if (edge[p].v! = Pre) INITDEPFA (edge[p].v,lay,s,d+1)    ;    }}void initpa (int n,int lay) {int i,j; for (j = 1;j < Maxm; ++j) {for (i = 1;i <= n; ++i) {if (pa[lay][i][j-1]! =-1  ) Pa[lay][i][j] = pa[lay][pa[lay][i][j-1]][j-1];              else Pa[lay][i][j] =-1; }}}int querykthpoint (int u,int k,int lay) {for (int i = maxm-1;i >= 0 && k;-i) {if (K >= (    1<<i)) U = pa[lay][u][i],k-= (1<<i); } return u;}    Queue<int> q;bool mark[maxn];int BFS (int s) {memset (mark,false,sizeof (Mark));    Mark[s] = true;    Q.push (s);        while (q.empty () = = False) {s = Q.front ();        Q.pop (); for (int p = head[s];p! =-1; p = edge[p].next) if (mark[edge[p].v] = = False) Q.push (EDGE[P].V), mark[    s] = true; } return s;}    int main () {int i,u,v,n,m,a,k;        while (scanf ("%d%d", &n,&m)! = EOF) {memset (head,-1,sizeof (head));        Top = 0;            for (i = 1;i < n; ++i) {scanf ("%d%d", &u,&v);            Link (U,V);        Link (V,u);        } u = BFS (v = BFS (1));        INITDEPFA (u,0);        INITPA (n,0);        INITDEPFA (v,1); INITPA (n,1);            while (m--) {scanf ("%d%d", &a,&k);            if (Dep[0][a] >=k) printf ("%d\n", Querykthpoint (a,k,0));            else if (Dep[1][a] >= k) printf ("%d\n", Querykthpoint (a,k,1));        else printf ("0\n"); }} return 0;}

diameter and multiplication of URAL 1752 tree 2 Trees