CF321C Ciel the Commander 题解 点分治

题目链接：http://codeforces.com/problemset/problem/321/C

解题思路：

点分治模板题。

每次找到重心给他分配一个字符，分治往下走的时候分配的字符ASCII码 $+1$ 即可。

示例程序：

#include <bits/stdc++.h>
using namespace std;
const int maxn = 1e5 + 5;

vector<int> g[maxn];
int n;
bool vis[maxn];
char id[maxn];

int get_size(int u, int p) {
    if (vis[u]) return 0;
    int sum = 1;
    for (auto v : g[u])
        if (v != p)
            sum += get_size(v, u);
    return sum;
}

int get_wc(int u, int p, int tot, int &wc) {
    if (vis[u]) return 0;
    int sum = 1, ms = 0;
    for (auto v : g[u]) {
        if (v == p) continue;
        int tmp = get_wc(v, u, tot, wc);
        ms = max(ms, tmp);
        sum += tmp;
    }
    ms = max(ms, tot - sum);
    if (ms <= tot / 2) wc = u;
    return sum;
}

void dfs(int u, char c) {
    if (vis[u]) return;
    get_wc(u, -1, get_size(u, -1), u);
    vis[u] = true;
    id[u] = c;
    for (auto v : g[u])
        dfs(v, c+1);
}

int main() {
    scanf("%d", &n);
    for (int i = 1; i < n; i++) {
        int u, v;
        scanf("%d%d", &u, &v);
        g[u].push_back(v);
        g[v].push_back(u);
    }
    dfs(1, 'A');
    for (int i = 1; i <= n; i++)
        printf("%c ", id[i]);
    return 0;
}