CF455C Civilization

嘟嘟嘟




水题一道，某谷又恶意评分。




合并无非是将两棵树的直径的中点连一块，记原来两棵树的直径为\(d_1, d_2\)，那么新的树的直径就是\(max(d_1, d_2, \lceil \frac{d_1}{2} \rceil + \lceil \frac{d_2}{2} \rceil + 1)\)，用并查集合并，更新即可。

#include<cstdio>
#include<iostream>
#include<cmath>
#include<algorithm>
#include<cstring>
#include<cstdlib>
#include<cctype>
#include<vector>
#include<stack>
#include<queue>
#include<assert.h>
using namespace std;
#define enter puts("")
#define space putchar(' ')
#define Mem(a, x) memset(a, x, sizeof(a))
#define In inline
typedef long long ll;
typedef double db;
const int INF = 0x3f3f3f3f;
const db eps = 1e-8;
const int maxn = 3e5 + 5;
In ll read()
{
  ll ans = 0;
  char ch = getchar(), last = ' ';
  while(!isdigit(ch)) last = ch, ch = getchar();
  while(isdigit(ch)) ans = (ans << 1) + (ans << 3) + ch - '0', ch = getchar();
  if(last == '-') ans = -ans;
  return ans;
}
In void write(ll x)
{
  if(x < 0) x = -x, putchar('-');
  if(x >= 10) write(x / 10);
  putchar(x % 10 + '0');
}
In void MYFILE()
{
#ifndef mrclr
  freopen(".in", "r", stdin);
  freopen(".out", "w", stdout);
#endif
}

int n, m, Q;
struct Edge
{
  int nxt, to;
}e[maxn << 1];
int head[maxn], ecnt = -1;
In void addEdge(int x, int y)
{
  e[++ecnt] = (Edge){head[x], y};
  head[x] = ecnt;
}

int p[maxn];
In int Find(int x) {return x == p[x] ? x : p[x] = Find(p[x]);}

int Max[maxn], dia[maxn];
In void dfs(int now, int _f, int id)
{
  p[now] = id;
  int Max1 = 0, Max2 = 0;
  for(int i = head[now], v; ~i; i = e[i].nxt)
    {
      if((v = e[i].to) == _f) continue;
      dfs(v, now, id);
      if(Max[v] + 1 > Max1) Max2 = Max1, Max1 = Max[v] + 1;
      else if(Max[v] + 1 > Max2) Max2 = Max[v] + 1;
    }
  Max[now] = Max1;
  dia[id] = max(dia[id], Max1 + Max2);
}

int main()
{
  //MYFILE();
  Mem(head, -1);
  n = read(), m = read(), Q = read();
  for(int i = 1; i <= m; ++i)
    {
      int x = read(), y = read();
      addEdge(x, y), addEdge(y, x);
    }
  for(int i = 1; i <= n; ++i) if(!p[i]) dfs(i, 0, i);
  for(int i = 1; i <= Q; ++i)
    {
      int op = read(), x = read();
      if(op == 1) write(dia[Find(x)]), enter;
      else
	{
	  int y = read();
	  int px = Find(x), py = Find(y);
	  if(px == py) continue;
	  p[px] = py;
	  dia[py] = max(max(dia[px], dia[py]), (dia[px] + 1) / 2 + (dia[py] + 1) / 2 + 1);
	}
    }
  return 0;
}