# Codeforces 455C C. Civilization (diameter of tree-shaped dp+ tree + and check set)

Source: Internet
Author: User

Codeforces 455C

Main topic:

Given some points, the initial existence of some edges between them, gives two operations, the first one is to query the diameter of the tree in which the point resides, and the other is to merge two trees, requiring the smallest diameter of the merged tree.

Topic Analysis:
• First calculate the diameter of the tree in the connected block before the operation, that is, Dfs once, find the deepest point of depth, and then search from this point, find the furthest distance is the diameter of this tree, because it can be proved from the root of the deepest point of the depth of the tree must be the diameter of an endpoint, Because it can reach the point of the sub-large depth or find the diameter of the tree with its common ancestor not at the root.
• And then every time we merge, we can know that the diameter of the new tree is max{max{ L 1 , L 2 },l 1 + 1 2 +l 2 + 1 2 +1}
• Then use and check the record connected block.
AC Code:
``#include <iostream>#include <cstring>#include <cstdio>#include <vector>#include <algorithm>#define MAX 300007using namespace STD;intN,m,q; vector<int>E[max];intFa[max];intAns[max];voidClear () { for(inti =0; i < MAX; i++) e[i].clear (); for(inti =1; i < MAX; i++) Fa[i] = i;}voidAdd (intU,intV) {e[u].push_back (v); E[v].push_back (u);}int_find (intx) {returnx = = Fa[x]?x:fa[x] = _find (Fa[x]);}void_union (intXintYintf) {x = _find (x); y = _find (y);if(x > Y) Swap (x, y); Fa[y] = x;if(f)return;intxx = ans[x];intyy = Ans[y]; ANS[X] = max (max (xx, yy), (xx+1)/2+ (yy+1)/2+1);}BOOLUsed[max];BOOLMark[max];intPp,dis;voidDFS (intU,intDintP) {if(d > Dis)        {dis = D;    pp = u; } for(inti =0; I < e[u].size (); i++) {intv = e[u][i];if(v = = p)Continue; DFS (V, d+1, u); }}intMain () { while( ~scanf("%d%d%d", &n, &m, &q)) {clear ();intX, Y, Z for(inti =0; I < m; i++) {scanf("%d%d", &x, &y);            Add (x, y); _union (x, Y,1); }memset(Used,0,sizeof(used)); for(inti =1; I <= N; i++) {intx = _find (i);if(Used[x])Continue; pp = dis =-1; USED[X] =true; DFS (x,1, -1); dis =0; DFS (PP,0, -1);        Ans[x] = dis; } for(inti =0; i < Q; i++) {scanf("%d", &z);if(Z = =1)            {scanf("%d", &x);printf("%d\n", Ans[_find (x)]); }Else{scanf("%d%d", &x, &y);if(_find (x) = = _find (y))Continue; _union (x, Y,0); }        }    }}``

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Codeforces 455C C. Civilization (diameter of tree-shaped dp+ tree + and check set)

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