Submission #807195

#	Time	Username	Problem	Language	Result	Execution time	Memory
807195		caganyanmaz	Group Photo (JOI21_ho_t3)	C++17	100 / 100	164 ms	165244 KiB

Main

#include <bits/stdc++.h>
using namespace std;
void calculate_prefix();

constexpr static int INF = 1e8;
constexpr static int MXSIZE = 5000;
int prefix[MXSIZE+1][MXSIZE+1], v[MXSIZE], dp[MXSIZE+1][MXSIZE+1], n, p[MXSIZE];
int get(int x1, int y1, int x2, int y2);

int main()
{
        cin >> n;
        for (int i = 0; i < n; i++)
        {
                cin >> v[i];
                v[i]--;
                p[v[i]] = i;
        }
        for (int i = 0; i < n; i++)
                prefix[i+1][v[i]+1] = 1;
        calculate_prefix();
        dp[0][0] = p[0];
        for (int i = 1; i < n; i++)
        {
                dp[i][i] = INF;
                for (int j = 0; j < i; j++)
                        dp[i][i] = min(dp[i][i], dp[i-1][j]);
                dp[i][i] += get(0, i, p[i], n);
                for (int j = 0; j < i; j++)
                        dp[i][j] = dp[i-1][j] - get(p[i], j, n, i) + get(0, j, p[i], n);
        }
        int best = INF;
        for (int i = 0; i < n; i++)
                best = min(best, dp[n-1][i]);
#ifdef DEBUGGING
        for (int i = 0; i < n; i++)
                for (int j = 0; j <= i; j++)
                        cout << (i+1) << " " << (j+1) << ": " << dp[i][j] << "\n";
#endif
        cout << best <<"\n";



}

void calculate_prefix() // O(n^2)
{
        for (int i = 1; i <= n; i++)
                for (int j = 1; j <= n; j++)
                        prefix[i][j] += prefix[i][j-1] + prefix[i-1][j] - prefix[i-1][j-1];
}


int get(int x1, int y1, int x2, int y2) // O(1)
{
        return prefix[x2][y2] - prefix[x2][y1] - prefix[x1][y2] + prefix[x1][y1];
}

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