Submission #1091039

#	Time	Username	Problem	Language	Result	Execution time	Memory
1091039		yogesh_sane	Group Photo (JOI21_ho_t3)	C++17	44 / 100	5086 ms	6740 KiB

Main

#include <iostream>
#include <vector>
#include <algorithm>
#include <numeric>
#include <queue>
using namespace std;

int n;
vector<int>a, idx;
vector<int>p;
int const inf = 1e9;
vector<int>dp;
vector<vector<int>>dpcost;

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);
}
int cost(int pos, int val){
    if(dpcost[pos][val] != -1)
        return dpcost[pos][val];
    //cout << "cost(" << pos << ',' << val << ")\n";
    iota(p.begin(), p.end(), 0);
    reverse(p.begin()+pos, p.begin()+val+1);
    int inv = 0;
    for(int i = pos; i <= val; i++){
        if(i == pos){
            inv += query_left(i, val+1, n);
            inv += query_right(i, i+1, val);
        }else if(i == val){
            //inv += query_left(i, pos, i-1);
            inv += query_left(i, val+1, n);
        }else{
            //inv += query_left(i, pos, i-1);
            inv += query_left(i, val+1, n);
            inv += query_right(i, i+1, val);
            //inv += query_right(i, 1, pos-1);
        }
    }

    // int inv2 = 0;
    // for(int i = pos; i <= val; i++){
    //     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]))
    //            inv2++;
    //     }
    // }
    //cout << inv << ' ' << inv2 << endl;
    return dpcost[pos][val] = inv;
}

int solve(int k){
    if(k > n)
        return 0;
    if(dp[k] != -1)
        return dp[k];
    //cout << "solve(" << k <<")" << endl;
    int ans = inf;    
    for(int i = k; i <= n; i++){
        ans = min(ans, cost(k, i) + solve(i+1));
    }
    return dp[k] = ans;
}
int main(){
    cin >> n;
    a.resize(n+1);
    p.resize(n+1);
    idx.resize(n+1);
    dp.resize(n+1, -1);
    dpcost.resize(n+1, vector<int>(n+1, -1));
    for(int i = 1; i <= n; i++){
        cin >> a[i];
        idx[a[i]] = i;
    }
    precalc_cost();
    cout << solve(1) << '\n';
    return 0;
}

• Subtask 1: 5 / 5
• Subtask 2: 7 / 7
• Subtask 3: 32 / 32
• Subtask 4: 0 / 20
• Subtask 5: 0 / 36