zroj#398. "18 Increase 7" Random walk (expected DP tree DP)

Test instructions

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Give a tree to find the maximum value of the desired distance between any two points

Sol

A more halal question.

Set \ (f[x]\) indicates the desired number of steps from \ (x\) to the father of \ (x\)

\ (g[x]\) indicates the desired number of steps coming from the father

\ (d[x]\) indicates the degree of the \ (x\) node

Not difficult to get the equation \ (f[x] = \sum_{to \in son[x]} F[to] + d[x]\)

\ (G[x] = g[fa[x]] + \sum_{to \in son[fa[x]] \text{and} to \not = x} F[to] + d[fa[x]]\)

Maintain up-down maximum value when calculating

Of course, careful observation is not difficult to find \ (f[x]\) is the degree of all nodes in the subtree

\ (g[x]\) the degree of the node outside the subtree for the entire tree

Considering the contribution of each side is not difficult to get

\ (F[x] = 2 * siz[x]-1\)

\ (G[x] = 2 * (n-siz[x])-1\)

#include <bits/stdc++.h> #define CHMAX (A, b) (A = a > B a:b) #define LL Long Long const int MAXN = 1e5 + 10;inli    NE int read () {char c = getchar (); int x = 0, f = 1;    while (C < ' 0 ' | | c > ' 9 ') {if (c = = '-') f =-1; c = GetChar ();}    while (c >= ' 0 ' && C <= ' 9 ') x = x * ten + C-' 0 ', C = GetChar (); return x * f;}  Std::vector<int> v[maxn];int N, UP[MAXN], DOWN[MAXN], D[MAXN], Siz[maxn], ans, f[maxn], g[maxn];void dfs3 (int x, int    FA) {siz[x] = 1;        for (int i = 0, to; i < v[x].size (); i++) {if (to = v[x][i]) = = FA) continue;        DFS3 (to, X);                SIZ[X] + = siz[to];        Ans = std::max (ans, Std::max (up[x] + g[to] + down[to], down[x] + f[to] + up[to]));        Chmax (Up[x], up[to] + f[to]);    Chmax (Down[x], down[to] + g[to]);    Chmax (ans, up[x] + down[x]);    } F[x] = (Siz[x] << 1)-1; G[X] = ((n-siz[x) << 1)-1;}    int main () {N = read (); for (int i = 1; i < N; i++) {int x = Read (), y = Read (); d[x]++;        d[y]++; V[x].push_back (y);     V[y].push_back (x);    } dfs3 (1, 0); printf ("%lld", ans);    Puts (". 00000"); return 0;}

zroj#398. "18 Increase 7" Random walk (expected DP tree DP)