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  • Codeforces 293E Close Vertices 点分治 + 树状数组

    点分治之后用树状数组维护个数。

    #include<bits/stdc++.h>
    #define LL long long
    #define LD long double
    #define ull unsigned long long
    #define fi first
    #define se second
    #define mk make_pair
    #define PLL pair<LL, LL>
    #define PLI pair<LL, int>
    #define PII pair<int, int>
    #define SZ(x) ((int)x.size())
    #define ALL(x) (x).begin(), (x).end()
    #define fio ios::sync_with_stdio(false); cin.tie(0);
    
    using namespace std;
    
    const int N = 1e5 + 7;
    const int inf = 0x3f3f3f3f;
    const LL INF = 0x3f3f3f3f3f3f3f3f;
    const int mod = 998244353;
    const double eps = 1e-8;
    const double PI = acos(-1);
    
    template<class T, class S> inline void add(T& a, S b) {a += b; if(a >= mod) a -= mod;}
    template<class T, class S> inline void sub(T& a, S b) {a -= b; if(a < 0) a += mod;}
    template<class T, class S> inline bool chkmax(T& a, S b) {return a < b ? a = b, true : false;}
    template<class T, class S> inline bool chkmin(T& a, S b) {return a > b ? a = b, true : false;}
    
    int n, l, w;
    vector<PII> G[N];
    bool ban[N];
    int son[N];
    LL ans;
    
    struct Bit {
        int a[N];
        inline void modify(int x, int v) {
            for(int i = x; i < N; i += i & -i)
                a[i] += v;
        }
        inline int sum(int x) {
            int ans = 0;
            for(int i = x; i; i -= i & -i)
                ans += a[i];
            return ans;
        }
        inline int query(int L, int R) {
            if(L > R) return 0;
            return sum(R) - sum(L - 1);
        }
    } bit;
    
    int getSubTreeSize(int u, int fa) {
        son[u] = 1;
        for(auto &e : G[u]) {
            if(e.se == fa || ban[e.se]) continue;
            son[u] += getSubTreeSize(e.se, u);
        }
        return son[u];
    }
    
    PII getSubTreeCenter(int u, int fa, int all) {
        PII res = mk(inf, -1);
        int s = 1, m = 0;
        for(auto &e : G[u]) {
            if(e.se == fa || ban[e.se]) continue;
            res = min(res, getSubTreeCenter(e.se, u, all));
            m = max(m, son[e.se]);
            s += son[e.se];
        }
        m = max(m, all - s);
        res = min(res, mk(m, u));
        return res;
    }
    
    void getDis(int u, int fa, int ld, int wd, vector<PII> &ds) {
        if(ld <= l && wd <= w) ans++;
        ds.push_back(mk(wd, ld));
        for(auto& e : G[u]) {
            if(e.se == fa || ban[e.se]) continue;
            getDis(e.se, u, ld + 1, wd + e.fi, ds);
        }
    }
    
    LL calc(vector<PII> &ds) {
        LL ans = 0;
        int n = ds.size();
        if(n <= 1) return 0;
        sort(ds.begin(), ds.end());
        for(auto &t : ds) bit.modify(t.se, 1);
        for(int i = 0, j = n - 1; i < n && i <= j; i++) {
            while(ds[i].fi + ds[j].fi > w && i <= j) {
                bit.modify(ds[j].se, -1);
                j--;
            }
            if(i > j) break;
            bit.modify(ds[i].se, -1);
            if(ds[i].se <= l) ans += bit.sum(l - ds[i].se);
        }
        return ans;
    }
    
    void solveSubPro(int u) {
        getSubTreeSize(u, 0);
        int s = getSubTreeCenter(u, 0, son[u]).se;
        ban[s] = true;
        vector<PII> ds, tds;
        for(auto &e : G[s]) {
            if(ban[e.se]) continue;
            tds.clear();
            getDis(e.se, s, 1, e.fi, tds);
            ans -= calc(tds);
            ds.insert(ds.end(), tds.begin(), tds.end());
        }
        ans += calc(ds);
        for(auto &e : G[s]) {
            if(ban[e.se]) continue;
            solveSubPro(e.se);
        }
    }
    
    int main() {
        scanf("%d%d%d", &n, &l, &w);
        for(int i = 1; i < n; i++) {
            int p, w;
            scanf("%d%d", &p, &w);
            G[p].push_back(mk(w, i + 1));
            G[i + 1].push_back(mk(w, p));
        }
        solveSubPro(1);
        printf("%lld
    ", ans);
        return 0;
    }
    
    /*
    */
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  • 原文地址:https://www.cnblogs.com/CJLHY/p/10987427.html
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