Submission #809080

#	Time	Username	Problem	Language	Result	Execution time	Memory
809080		AndrijaM	Exam (eJOI20_exam)	C++14	100 / 100	228 ms	99572 KiB

exam

#include <iostream>
#include <algorithm>
#include <cstring>
#include <vector>
#include <set>
#include <map>
#include <stack>
using namespace std;
typedef long long ll;
const int maxn = 1e5 + 10;
const int INF = 2e9;
int n;
int a[maxn], b[maxn];
int L[maxn], R[maxn];
int segment_tree[4 * maxn];
void solve_subtask2() {
    int x = b[0];
    int res = 0;
    for(int i = 0; i < n; i++) {
        if(a[i] == x) {
            res++;
            int j = i - 1;
            while(j >= 0 and a[j] <= x) {
                j--;
                res++;
            }
            j = i + 1;
            while(j < n and a[j] <= x) {
                res++;
                j++;
            }
            i = j - 1;
        }
    }
    cout << res << endl;
}
int dp[5005][5005];
int rec(int i, int j) {
    if(i < 0 or j < 0) {
        return 0;
    }
    if(dp[i][j] != -1) {
        return dp[i][j];
    }
    int res = 0;
    if(a[i] == b[j] and L[i] < j and R[i] > j) {
        res = max(res, rec(i, j - 1) + 1);
    }
    res = max(res, rec(i - 1, j));
    res = max(res, rec(i, j - 1));
    return dp[i][j] = res;
}
void build_tree(int L, int R, int node) {
    if(L == R) {
        segment_tree[node] = 0;
        return;
    }
    int middle = (L + R) / 2;
    build_tree(L, middle, 2 * node);
    build_tree(middle + 1, R, 2 * node + 1);
    segment_tree[node] = max(segment_tree[2 * node], segment_tree[2 * node + 1]);
}
int query(int i, int j, int L, int R, int node) {
    // L  R i L R j L R
    if(i <= L and R <= j) {
        return segment_tree[node];
    }
    if(R < i or j < L) {
        return 0;
    }
    int middle = (L + R) / 2;
    return max(query(i, j, L, middle, 2 * node), query(i, j, middle + 1, R, 2 * node + 1));
}
void update(int idx, int new_value, int L, int R, int node) {
    if(L == R) {
        segment_tree[node] = new_value;
        return;
    }
    int middle = (L + R) / 2;
    if(idx <= middle) {
        update(idx, new_value, L, middle, 2 * node);
    }
    else {
        update(idx, new_value, middle + 1, R, 2 * node + 1);
    }
    segment_tree[node] = max(segment_tree[2 * node], segment_tree[2 * node + 1]);
}
int main() {
    ios_base::sync_with_stdio(false);
    cin >> n;
    set<int> st;
    vector<int> t(n + 5);
    for(int i = 0; i < n; i++) {
        cin >> a[i];
        t[i + 1] = a[i];
    }
    for(int i = 0; i < n; i++) {
        cin >> b[i];
        st.insert(b[i]);
    }
    t[0] = INF;
    t[n + 1] = INF;
    stack<int> s;
    s.push(0);
    for(int i = 1; i <= n; i++) {
        while(t[s.top()] <= t[i]) {
            s.pop();
        }
        L[i - 1] = s.top() - 1;
        s.push(i);
    }
    while(!s.empty()) {
        s.pop();
    }
    s.push(n + 1);
    for(int i = n; i > 0; i--) {
        while(t[s.top()] <= t[i]) {
            s.pop();
        }
        R[i - 1] = s.top() - 1;
        s.push(i);
    }
    
    if((int) st.size() == 1) {
        solve_subtask2();
        return 0;
    }
    else if(n <= 5005){
        memset(dp, -1, sizeof dp);
        cout << rec(n - 1, n - 1) << endl;
    }
    else {
        build_tree(0, n - 1, 1);
        map<int, int> m;
        for(int i = 0; i < n; i++) {
            m[a[i]] = i;
        }
        
        for(int i = 0; i < n; i++) {
            map<int, int>::iterator it = m.find(b[i]);
            if(it != m.end()) {
                int idx = it->second;
                if(L[idx] < i and i < R[idx]) {
                    int dp = query(0, idx, 0, n - 1, 1);
                    update(idx, dp + 1, 0, n - 1, 1);
                }
            }
        }
        cout << query(0, n - 1, 0, n - 1, 1) << endl;
    }
    
    return 0;
}
 

• Subtask 1: 14 / 14
• Subtask 2: 12 / 12
• Subtask 3: 13 / 13
• Subtask 4: 23 / 23
• Subtask 5: 16 / 16
• Subtask 6: 22 / 22