【BZOJ 1036】[ZJOI2008]树的统计Count

【题目链接】:http://www.lydsy.com/JudgeOnline/problem.php?id=1036

【题意】

【题解】

树链剖分入门题;
每一条链维护一个线段树就好;
uppest数组维护这条链的最顶端的元素;
一条链一条链的往上走;直到两个点在同一条链里面了
balabala

【完整代码】

#include <bits/stdc++.h>
using namespace std;
#define lson l,m,rt<<1
#define rson m+1,r,rt<<1|1
#define LL long long
#define rep1(i,a,b) for (int i = a;i <= b;i++)
#define rep2(i,a,b) for (int i = a;i >= b;i--)
#define mp make_pair
#define pb push_back
#define fi first
#define se second
#define rei(x) scanf("%d",&x)
#define rel(x) scanf("%lld",&x)
#define ref(x) scanf("%lf",&x)

typedef pair<int, int> pii;
typedef pair<LL, LL> pll;

const int dx[9] = { 0,1,-1,0,0,-1,-1,1,1 };
const int dy[9] = { 0,0,0,-1,1,-1,1,-1,1 };
const double pi = acos(-1.0);
const int N = 3e4+100;
const int INF = 3e4 + 200;

int n,fa[N],siz[N],dep[N],uppest[N],bh[N],cnt;
int v[N],sum[N<<2],mx[N<<2];
vector <int> G[N];

void in()
{
    rei(n);
    rep1(i, 1, n - 1)
    {
        int x, y;
        rei(x), rei(y);
        G[x].pb(y), G[y].pb(x);
    }
    rep1(i, 1, n)
        rei(v[i]);
}

void dfs1(int x)
{
    int len = G[x].size();
    siz[x] = 1;
    rep1(i, 0, len - 1)
    {
        int y = G[x][i];
        if (y == fa[x]) continue;
        fa[y] = x;
        dep[y] = dep[x] + 1;
        dfs1(y);
        siz[x] += siz[y];
    }

}

void dfs2(int x, int chain)
{
    int len = G[x].size();
    int k = 0;
    bh[x] = ++cnt;
    uppest[x] = chain;
    rep1(i, 0, len - 1)
    {
        int y = G[x][i];
        if (dep[y]>dep[x] && siz[y] > siz[k])
            k = y;
    }
    if (k == 0) return;
    dfs2(k, chain);
    rep1(i, 0, len - 1)
    {
        int y = G[x][i];
        if (dep[y] > dep[x] && y != k)
            dfs2(y, y);
    }
}

void updata(int pos, int val,int l, int r, int rt)
{
    if (l == r)
    {
        sum[rt] = mx[rt] = val;
        return;
    }
    int m = (l + r) >> 1;
    if (pos <= m)
        updata(pos, val,lson);
    else
        updata(pos, val,rson);
    sum[rt] = sum[rt << 1] + sum[rt << 1 | 1];
    mx[rt] = max(mx[rt << 1], mx[rt << 1 | 1]);
}

int query_max(int L, int R, int l, int r, int rt)
{
    if (L <= l && r <= R)
        return mx[rt];
    int m = (l + r) >> 1;
    int temp1 = -INF;
    if (L <= m)
        temp1 = max(temp1, query_max(L, R, lson));
    if (m < R)
        temp1 = max(temp1, query_max(L, R, rson));
    return temp1;
}

int get_max(int u, int v)
{
    int t = -3e4 - 100;
    while (uppest[u] != uppest[v])
    {
        if (dep[uppest[u]] < dep[uppest[v]])
            swap(u, v);
        t = max(t, query_max(bh[uppest[u]], bh[u], 1, n, 1));
        u = fa[uppest[u]];
    }
    if (dep[u] < dep[v])
        swap(u, v);
    t = max(t, query_max(bh[v], bh[u], 1, n, 1));
    return t;
}

int query_sum(int L, int R, int l, int r, int rt)
{
    if (L <= l && r <= R)
        return sum[rt];
    int m = (l + r) >> 1;
    int temp = 0;
    if (L <= m)
        temp += query_sum(L, R, lson);
    if (m < R)
        temp += query_sum(L, R, rson);
    return temp;
}

int get_sum(int u, int v)
{
    int t = 0;
    while (uppest[u] != uppest[v])
    {
        if (dep[uppest[u]] < dep[uppest[v]])
            swap(u, v);
        t += query_sum(bh[uppest[u]], bh[u], 1, n, 1);
        u = fa[uppest[u]];
    }
    if (dep[u] < dep[v])
        swap(u, v);
    t+=query_sum(bh[v], bh[u], 1, n, 1);
    return t;
}

void get_ans()
{
    rep1(i, 1, n)
        updata(bh[i], v[i],1, n, 1);
    int q;
    rei(q);
    char s[8];
    rep1(i, 1, q)
    {
        scanf("%s", s);
        if (s[0] == 'C')
        {
            int u, t;
            rei(u), rei(t);
            updata(bh[u], t, 1, n, 1);
        }
        else
        {
            int u, v;
            rei(u), rei(v);
            if (s[1] == 'M')
                printf("%d\n", get_max(u, v));
            else
                printf("%d\n", get_sum(u, v));
        }
    }
}

int main()
{
    //freopen("F:\\rush.txt", "r", stdin);

    in();
    dfs1(1);
    dfs2(1, 1);
    get_ans();
    //printf("\n%.2lf sec \n", (double)clock() / CLOCKS_PER_SEC);
    return 0;
}