Submission #587406

#	Time	Username	Problem	Language	Result	Execution time	Memory
587406		MohamedAliSaidane	Cat in a tree (BOI17_catinatree)	C++14	100 / 100	449 ms	47188 KiB

catinatree

#include<bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>

        using namespace __gnu_pbds;
        using namespace std;

        typedef tree<int,null_type,less<int>,rb_tree_tag,
        tree_order_statistics_node_update> indexed_set;

        typedef long long ll;
        typedef long double ld;

        ///#define int ll

        typedef pair<int,int> pii;
        typedef pair<ll,ll> pll;
        typedef pair<ld,ld> pld;

        typedef vector<int> vi;
        typedef vector<ll> vll;
        typedef vector<pii> vpi;
        typedef vector<pll> vpl;

        #define pb push_back
        #define popb pop_back
        #define pp pop_back
        #define pf push_front
        #define popf pop_front
        #define all(x) (x).begin(),(x).end()
        #define ff first
        #define ss second



        int nx[4] = {0,0,1,-1}, ny[4] = {1,-1,0,0};
        ll gcd(ll a , ll b) {return b ? gcd(b , a % b) : a ;}
        ll lcm(ll a , ll b) {return (a * b) / gcd(a , b);}


        const ll MOD =   998244353;

        const int nax = 2e5 + 4;
        int n, k;
        vi adj[nax];
        vi lay[nax];
        int d[nax], head[nax], minidis[nax], sp[nax][21], mark[nax],
        sz[nax];
        void dfs(int x, int p)
        {
            d[x] = d[p] + 1;
            sp[x][0] = p;
            lay[d[x]].pb(x);
            for(auto e: adj[x])
                if(e != p)
                    dfs(e,x);
        }
        void build()
        {
            for(int j=  1; j < 20; j ++)
                for(int i = 1; i <= n; i ++)
                    sp[i][j] = sp[sp[i][j-1]][j-1];

        }
        int jump(int a, int k)
        {
            for(int i = 0; i < 20; i ++)
                if((1 << i) & k)
                    a = sp[a][i];
            return a;
        }
        int lca(int a, int b)
        {
            if(d[a] < d[b])
                swap(a,b);
            a = jump(a, d[a] - d[b]);
            if(a == b)
                return a;
            for(int i=  19; i >= 0; i --)
                if(sp[a][i] != sp[b][i])
                    a = sp[a][i], b = sp[b][i];
            return sp[a][0];
        }
        int dist(int a, int b)
        {
            int c = lca(a,b);
            return d[a] + d[b] - 2 * d[c];
        }
        int subtreesz(int x, int p)
        {
            sz[x] = 1;
            for(auto e: adj[x])
            {
                if(e == p || mark[e])
                    continue;
                sz[x] += subtreesz(e,x);
            }
            return sz[x];
        }

        int centroid(int x, int p, int s)
        {
            for(auto e: adj[x])
            {
                if(e == p || mark[e])
                    continue;
                if(sz[e] > s/2)
                    return centroid(e,x,s);
            }
            return x;
        }
        int get_centroid(int x)
        {
            ///cout << x << endl;
            x = centroid(x,0,subtreesz(x,0));
            mark[x] = 1;
            for(auto e: adj[x])
            {
                if(mark[e])
                    continue;
                int c = get_centroid(e);
                head[c] = x;
            }
            return x;
        }
        int compute(int x)
        {
            int mini = MOD/2;
            int cur = x;
            while(cur != 0)
            {
                mini = min(mini,minidis[cur] + dist(cur,x));
                cur = head[cur];
            }
            return mini;
        }
        void update(int x)
        {
            int cur = x;
            while(cur != 0)
            {
                minidis[cur] = min(minidis[cur], dist(cur,x));
                cur = head[cur];
            }
        }
        void solve()
        {
            cin >> n >> k;
            for(int a= 2 ; a <= n ;a ++)
            {
                int b; cin >> b;
                b ++ ;
                adj[a].pb(b);
                adj[b].pb(a);
            }

            d[0] = -1;
            dfs(1,0);
            build();
            get_centroid(1);

            for(int i= 1 ; i <= n; i ++)
                minidis[i] = MOD/2;
            int ans = 0;
            for(int l= n - 1; l >= 0; l --)
            {
                for(auto e: lay[l])
                {
                    int mind = compute(e);
                    if(mind >= k)
                    {
                        ans ++;
                        update(e);
                    }
                }
            }
            cout << ans;
        }
        int32_t main()
        {
            ios::sync_with_stdio(false);
            cin.tie(0); cout.tie(0);
            int tt = 1; //cin >> tt;
            while(tt --)
                solve();
        }

• Subtask 1: 11 / 11
• Subtask 2: 40 / 40
• Subtask 3: 49 / 49