bzoj1776

点分治/贪心

对于点分治的理解不够深刻...点分治能统计树上每个点对的信息，那么这里就是统计同种颜色点对之间的最大距离，自然可以用点分

然后点分，每次统计最大距离，但是略微卡常...

还有一种贪心的方法，每种颜色必然选以某点为根最深的节点，计算出最深的节点，然后dfs，看每种颜色，然后和最深的节点计算距离

#include<bits/stdc++.h>
using namespace std;
const int N = 200010;
int n, top, root, k, top1;
vector<int> G[N];
int size[N], mx[N], mark[N], ans[N], st[N], st1[N], c[N], a[N], mx_deep[N], now_deep[N], vis[N], vis1[N];
namespace IO 
{
    const int Maxlen = N * 50;
    char buf[Maxlen], *C = buf;
    int Len;
    inline void read_in()
    {
        Len = fread(C, 1, Maxlen, stdin);
        buf[Len] = '';
    }
    inline void fread(int &x) 
    {
        x = 0;
        int f = 1;
        while (*C < '0' || '9' < *C) { if(*C == '-') f = -1; ++C; }
        while ('0' <= *C && *C <= '9') x = (x << 1) + (x << 3) + *C - '0', ++C;
        x *= f;
    }
    inline void read(int &x)
    {
        x = 0;
        int f = 1; char c = getchar();
        while(c < '0' || c > '9') { if(c == '-') f = -1; c = getchar(); }
        while(c >= '0' && c <= '9') { x = (x << 1) + (x << 3) + c - '0'; c = getchar(); }
        x *= f;
    }
    inline void read(long long &x)
    {
        x = 0;
        long long f = 1; char c = getchar();
        while(c < '0' || c > '9') { if(c == '-') f = -1; c = getchar(); }
        while(c >= '0' && c <= '9') { x = (x << 1ll) + (x << 3ll) + c - '0'; c = getchar(); }
        x *= f;
    } 
} using namespace IO;
void findroot(int u, int last, int tot)
{
    size[u] = 1;
    mx[u] = 0;
    for(int i = 0; i < G[u].size(); ++i)
    {
        int v = G[u][i];
        if(v == last || mark[v]) continue;
        findroot(v, u, tot);
        size[u] += size[v];
        if(size[v] > mx[u]) mx[u] = size[v];
    }
    mx[u] = max(mx[u], tot - mx[u]);
    if(mx[u] < mx[root]) root = u; 
}
void dfs(int u, int last, int deep)
{
    if(mx_deep[a[u]] == -1) st[++top] = a[u];
    mx_deep[a[u]] = max(mx_deep[a[u]], deep); 
    for(int i = 0; i < G[u].size(); ++i)
    {
        int v = G[u][i];
        if(v == last || mark[v]) continue;
        dfs(v, u, deep + 1);
    }
}
int get_size(int u, int last)
{
    int ret = 1;
    for(int i = 0; i < G[u].size(); ++i)
    {
        int v = G[u][i];
        if(v == last || mark[v]) continue;
        ret += get_size(v, u);
    }
    return ret;
}
void divide(int u)
{
    root = 0;
    findroot(u, 0, get_size(u, 0));
    mark[root] = 1;
    now_deep[a[root]] = 0;
    st1[++top1] = a[root];
    for(int i = 0; i < G[root].size(); ++i)
    {
        int v = G[root][i];
        if(mark[v]) continue;
        dfs(v, root, 1);
        if(mx_deep[a[root]] == -1) st[++top] = a[root], mx_deep[a[root]] = 0;
        for(int j = top; j; --j) if(now_deep[st[j]] != -1) ans[st[j]] = max(ans[st[j]], now_deep[st[j]] + mx_deep[st[j]]);
        while(top) 
        {
            if(now_deep[st[top]] == -1) st1[++top1] = st[top];
            now_deep[st[top]] = max(now_deep[st[top]], mx_deep[st[top]]);
            mx_deep[st[top--]] = -1;
        }
    }
    while(top1) now_deep[st1[top1--]] = -1; 
    for(int i = 0, now = root; i < G[now].size(); ++i) 
    {
        int v = G[now][i];
        if(mark[v]) continue;
        divide(v);
    }
}
int main()
{
    memset(now_deep, -1, sizeof(now_deep));
    memset(mx_deep, -1, sizeof(mx_deep));
    read_in();
    fread(n);
    fread(k);
    for(int i = 1; i <= n; ++i)
    {
        int u;
        fread(a[i]);
        fread(u);
        if(u) { G[u].push_back(i); G[i].push_back(u); }
    }
    mx[0] = 1 << 29;
    divide(1);
    for(int i = 1; i <= k; ++i) printf("%d
", ans[i]);
    return 0;
}