Submission #986311

#	Time	Username	Problem	Language	Result	Execution time	Memory
986311		yanndev	Group Photo (JOI21_ho_t3)	C++17	100 / 100	336 ms	852 KiB

Main

#include <bits/stdc++.h>
#define int long long
using namespace std;

int n;
int dp[5044];

void add(vector<int>& bit, int idx, int val) {
    for (int i = idx + 1; i <= (int)bit.size(); i += (i & -i))
        bit[i] += val;
}

int sum(vector<int>& bit, int idx) {
    int ans = 0;
    for (int i = idx + 1; i > 0; i -= (i & -i))
        ans += bit[i];
    return ans;
}

signed main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    
    cin >> n;

    vector<int> ls (n + 1);
    for (int i = 1; i <= n; i++)
        cin >> ls[i];

    for (int i = 0; i <= n; i++)
        dp[i] = 1e16;
    dp[0] = 0;

    for (int l = 0; l + 1 <= n; l++) {
        vector<int> bit (n + 2, 0);
        vector<int> pos (n + 1, 0);

        /*
            we used everything from 1 to l
        */

        int cur = l + 1;
        for (int i = 1; i <= n; i++)
            if (ls[i] > l)
                pos[ls[i]] = cur++;

        int s = 0;
        int inv = 0;
        for (int r = l + 1; r <= n; r++) {
            // from l + 2 to r + 1
            s += pos[r];
            inv += sum(bit, pos[r]);
            add(bit, pos[r], 1);
            //cout << "from " << l << " to " << r << " s " << s << ' ' << inv << '\n';
            dp[r] = min(dp[r], dp[l] + inv + s - ((r * (r + 1) / 2) - (l * (l + 1) / 2)));
        }
    }

    cout << dp[n] << '\n';
}

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