Submission #1091185

#	Time	Username	Problem	Language	Result	Execution time	Memory
1091185		yogesh_sane	Group Photo (JOI21_ho_t3)	C++17	100 / 100	3623 ms	135360 KiB

Main

#include <iostream>
#include <vector>
#include <algorithm>
#include <numeric>
#include <queue>
using namespace std;
 
int n;
int const inf = 1e9;
vector<int>a, idx;
vector<int>cost;
int total_cost;
vector<vector<int>>left_num, right_num;
void precalc_cost(){
    left_num.resize(n+1);
    right_num.resize(n+1);
    for(int i = 1; i <= n; i++){
        for(int j = i+1; j <=n; j++){
            left_num[a[j]].push_back(a[i]);
        }
    }
    for(int i = n; i >= 1; i--){
        for(int j = i-1; j >= 1; j--){
            right_num[a[j]].push_back(a[i]);
        }
    }
    for(int i = 1; i <= n; i++){
        sort(left_num[i].begin(), left_num[i].end());
        sort(right_num[i].begin(), right_num[i].end());
    }
}
int query(vector<int> &v, int l, int r){
    if(l > r)
        return 0;
    //numbers less than or equal to r
    int num_r = lower_bound(v.begin(), v.end(), r+1)-v.begin();
    //numbers less than l
    int num_l = lower_bound(v.begin(), v.end(),l)-v.begin();
    return num_r-num_l;
}
int query_left(int num, int l, int r){
    return query(left_num[num], l, r);
}
int query_right(int num, int l, int r){
    return query(right_num[num], l, r);
}
void calculate_cost(int val){
    vector<int>p(n+1);
    // iota(p.begin(), p.end(), 0);
    // reverse(p.begin()+1, p.begin()+val+1);
    // for(int i = val; i >= 1; i--){
    //     int inv = 0;
    //     for(int j = i+1; j <= n; j++){
    //         if((p[i] < p[j] && idx[i] > idx[j]) ||
    //            (p[i] > p[j] && idx[i] < idx[j]))
    //            inv++;
    //     }
    //     cost.push_back(inv);
    //     total_cost += inv;
    // }

    iota(p.begin(), p.end(), 0);
    reverse(p.begin()+1, p.begin()+val+1);
    int inv = 0;
    for(int i = val; i >= 1; i--){
        inv += query_left(i, val+1, n);
        inv += query_right(i, i+1, val);
        cost.push_back(inv);
        total_cost += inv;
    }
}
 
int main(){
    cin >> n;
    a.resize(n+1);
    idx.resize(n+1);
    vector<int>dp(n+1, inf);
    for(int i = 1; i <= n; i++){
        cin >> a[i];
        idx[a[i]] = i;
    }
    precalc_cost();
    dp[0] = 0;
    for(int i = 1; i <= n; i++){
        calculate_cost(i);
        for(int j = 1; j <= i; j++){
            // dp[i] = min(dp[i], dp[j-1] + total_cost);
            // total_cost -= cost.back();
            dp[i] = min(dp[i], dp[j-1] + cost.back());
            cost.pop_back();
        }
    }
    cout << dp[n] << '\n';
    return 0;
}

• Subtask 1: 5 / 5
• Subtask 2: 7 / 7
• Subtask 3: 32 / 32
• Subtask 4: 20 / 20
• Subtask 5: 36 / 36