Submission #769233

#	Time	Username	Problem	Language	Result	Execution time	Memory
769233		danikoynov	Cat Exercise (JOI23_ho_t4)	C++14	21 / 100	238 ms	19576 KiB

Main

#include<bits/stdc++.h>
#define endl '\n'

using namespace std;
typedef long long ll;

void speed()
{
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    cout.tie(NULL);
}

const int maxn = 2e5 + 10;

int n, a[maxn], used[maxn], dp[maxn], pos[maxn];
vector < int > adj[maxn];

int rec(int val)
{
    if (used[val])
        return dp[val];
    used[val] = 1;
    int left = 0, right = n + 1;
    for (int i = n; i > val; i --)
    {
        if (pos[i] > pos[val])
        {
            right = min(right, pos[i]);
        }
        else
        {
            left = max(left, pos[i]);
        }
    }

    int mx = -1;
    for (int i = pos[val] + 1; i < right; i ++)
    {
        if (a[i] > mx)
        {
            mx = a[i];
            dp[val] = max(dp[val], i - pos[val] + rec(a[i]));
        }
    }
    mx = -1;
    for (int i = pos[val] - 1; i > left; i --)
    {
        if (a[i] > mx)
        {
            mx = a[i];
            dp[val] = max(dp[val], pos[val] - i + rec(a[i]));
        }
    }
    return dp[val];
}

int dfs(int v, int p, int mx, int dis, int val)
{
    if (mx > val)
        return 0;

    int ans = 0;
    if (a[v] == mx)
        ans = max(ans, dis + dp[v]);

    for (int u : adj[v])
    {
        if (u == p)
            continue;
        ans = max(ans, dfs(u, v, max(mx, a[u]), dis + 1, val));

    }

    return ans;
}

int bef[maxn], aft[maxn];

pair < int, int > tree[4 * maxn];

void build_tree(int root, int left, int right)
{
    if (left == right)
    {
        tree[root] = {a[left], left};
        return;
    }

    int mid = (left + right) / 2;
    build_tree(root * 2, left, mid);
    build_tree(root * 2 + 1, mid + 1, right);

    tree[root] = max(tree[root * 2], tree[root * 2 + 1]);
}

pair < int, int > query(int root, int left, int right, int qleft, int qright)
{
    if (left > qright || right < qleft)
        return {-1, -1};

    if (left >= qleft && right <= qright)
        return tree[root];

    int mid = (left + right) / 2;
    return max(query(root * 2, left, mid, qleft, qright),
               query(root * 2 + 1, mid + 1, right, qleft, qright));
}

void solve()
{
    cin >> n;
    for (int i = 1; i <= n; i ++)
    {
        cin >> a[i];
        pos[a[i]] = i;
    }


    for (int i = 1; i < n; i ++)
    {
        int v, u;
        cin >> v >> u;
        adj[v].push_back(u);
        adj[u].push_back(v);
    }


    /**if (n <= 5000)
    {
        for (int i = 1; i <= n; i ++)
        {
            int v = pos[i];
            for (int u : adj[v])
            {
                dp[v] = max(dp[v], dfs(u, v, a[u], 1, a[v]));
            }
            ///cout << v << " : " << dp[v] << endl;
        }


        cout << dp[pos[n]] << endl;
    }
    else*/
    {
        stack < int > st;
        for (int i = 1; i <= n; i ++)
        {
            while(!st.empty() && a[st.top()] < a[i])
                st.pop();

            if (!st.empty())
                bef[i] = st.top();
            ///cout << "stack " << i << " " << st.top() << endl;
            st.push(i);
        }

        while(!st.empty())
            st.pop();

        for (int i = n; i > 0; i --)
        {
            while(!st.empty() && a[st.top()] < a[i])
                st.pop();
            if (!st.empty())
                aft[i] = st.top();
            else
                aft[i] = n + 1;
            st.push(i);
        }
        build_tree(1, 1, n);
        for (int i = 1; i <= n; i ++)
        {
            int v = pos[i];
            ///cout << "now " << v << " " << bef[v] << " " <<aft[v] << endl;
            pair < int, int > lf = query(1, 1, n, bef[v] + 1, v - 1);
            pair < int, int > rf = query(1, 1, n, v + 1, aft[v] - 1);
            ///cout << v << " " << lf.second << " " << rf.second << endl;
            if (lf.first != -1)
            {
                ///cout << "here " << dp[lf.first] << " " << lf.first << endl;
                dp[v] = max(dp[v], dp[lf.second] + v - lf.second);
            }
            if (rf.first != -1)
                dp[v] = max(dp[v], dp[rf.second] + rf.second - v);
            //cout << dp[v] << endl;
        }
        cout << dp[pos[n]] << endl;
    }



}

int main()
{
    solve();
    return 0;
}
/**
5
5 3 2 1 4
1 2
2 3
3 4
4 5
*/

• Subtask 1: 7 / 7
• Subtask 2: 7 / 7
• Subtask 3: 7 / 7
• Subtask 4: 0 / 10
• Subtask 5: 0 / 20
• Subtask 6: 0 / 23
• Subtask 7: 0 / 26