HDU 5266 pog loves szh III-摩杜云开发者社区

Problem Description

Pog and Szh are playing games. Firstly Pog draw a tree on the paper. Here we define 1 as the root of the tree. Then Szh choose some nodes from the tree. He wants Pog helps to find the least common ancestor(LCA) of these node. The question is too difficult for Pog. So he decided to simplify the problems. The nodes picked are consecutive numbers from li to ri ([li,ri]).

Hint : You should be careful about stack overflow !

Input

Several groups of data (no more than 3 groups,n≥10000 or Q≥10000).

The following line contains ans integers,n(2≤n≤300000).

AT The following n−1 line, two integers are bi and ci at every line, it shows an edge connecting bi and ci.

The following line contains ans integers,Q(Q≤300000).

AT The following Q line contains two integers li and ri(1≤li≤ri≤n).

Output

For each case,output Q integers means the LCA of [li,ri].

Sample Input

5 1 2 1 3 3 4 4 5 5 1 2 2 3 3 4 3 5 1 5

Sample Output

1 1 3 3 1

Hint

Be careful about stack overflow.

lca+rmq

#include<cstdio>
#include<cstring>
#include<vector>
#include<iostream>
#include<queue>
#include<algorithm>
#include<cmath>
#include<cstdlib>
#include<string>
using namespace std;
const int maxn = 300005;
int n, m, x, y, lc[maxn][20], dp[maxn][20], deep[maxn];
vector<int> t[maxn];

void bfs()
{
  queue<int> p;
  p.push(1);  deep[1] = 1;
  while (!p.empty())
  {
    int q = p.front();  p.pop();
    for (int i = 0; i < t[q].size(); i++)
    if (t[q][i] != lc[q][0])
    {
      lc[t[q][i]][0] = q;
      deep[t[q][i]] = deep[q] + 1;
      p.push(t[q][i]);
    }
  }
}

int lca(int a, int b)
{
  int i, j;
  if (deep[a]<deep[b]) swap(a, b);
  for (i = 0; (1 << i) <= deep[a]; i++);
  i--;
  for (j = i; j >= 0; j--)
    if (deep[a] - (1 << j) >= deep[b])
      a = lc[a][j];
  if (a == b)return a;
  for (j = i; j >= 0; j--)
  {
    if (lc[a][j] != -1 && lc[a][j] != lc[b][j])
    {
      a = lc[a][j];
      b = lc[b][j];
    }
  }
  return lc[a][0];
}

int query(int s, int v)
{
  int k = (int)(log((v - s + 1)*1.0) / log(2.0));
  return lca(dp[s][k], dp[v - (1 << k) + 1][k]);
}

int main()
{
  while (cin >> n)
  {
    memset(dp, -1, sizeof(dp));
    memset(lc, -1, sizeof(lc));
    for (int i = 1; i <= n; i++) 
    { 
      t[i].clear(); 
      dp[i][0] = i; 
      deep[i] = 0;
    }
    for (int i = 1; i < n; i++)
    {
      scanf("%d%d", &x, &y);
      t[x].push_back(y); 
      t[y].push_back(x);
    }
    bfs();
    
    for (int j = 1; (1 << j) <= n; j++)
      for (int i = 1; i <= n; i++)
        if (lc[i][j - 1] != -1) lc[i][j] = lc[lc[i][j - 1]][j - 1];
    
    for (int j = 1; (1 << j) <= n; j++)
      for (int i = 1; i <= n; i++)
      if (i + (1 << j) - 1 <= n)
      {
        dp[i][j] = lca(dp[i][j - 1], dp[i + (1 << (j - 1))][j - 1]);
      }

    cin >> m;
    while (m--)
    {
      scanf("%d%d", &x, &y);
      printf("%d\n", query(x, y));
    }
  }
}