Submission #685163

#	Time	Username	Problem	Language	Result	Execution time	Memory
685163		ethening	Group Photo (JOI21_ho_t3)	C++17	100 / 100	772 ms	196896 KiB

Main

#include "bits/stdc++.h"
#include <vector>
using namespace std;
using ll = long long;

const int INF = 1e9;

int n;
int a[5005];

vector<vector<int>> p1, p2;

void compute_p(vector<vector<int>>& p) {
	for (int i = 1; i <= n; i++) {
		for (int j = 1; j <= n; j++) {
			p[i][j] = p[i][j] + p[i][j - 1] + p[i - 1][j] - p[i - 1][j - 1];
		}
	}
}

int get_p(vector<vector<int>>& p, int l1, int r1, int l2, int r2) {
	return p[r1][r2] - p[l1 - 1][r2] - p[r1][l2 - 1] + p[l1 - 1][l2 - 1];
}

int main() {
	cin.tie(0)->sync_with_stdio(0);
	cin >> n;
	for (int i = 1; i <= n; i++) {
		cin >> a[i];
	}

	p1 = vector<vector<int>>(n + 5, vector<int>(n + 5, 0));
	p2 = vector<vector<int>>(n + 5, vector<int>(n + 5, 0));

	vector<int> dp(n + 5, INF);

	for (int i = 1; i <= n; i++) {
		for (int j = i + 1; j <= n; j++) {
			if (a[i] > a[j]) {
				++p1[a[i]][a[j]];
			}
			else if (a[i] < a[j]) {
				++p2[a[i]][a[j]];
			}
		}
	}

	// for (int i = 1; i <= n; i++) {
	// 	for (int j = 1; j <= n; j++) {
	// 		cout << p1[i][j] << " \n"[j == n];
	// 	}
	// }

	// cout << "\n";
	// for (int i = 1; i <= n; i++) {
	// 	for (int j = 1; j <= n; j++) {
	// 		cout << p2[i][j] << " \n"[j == n];
	// 	}
	// }


	compute_p(p1);
	compute_p(p2);

	// cout << "===\n";
	// for (int i = 1; i <= n; i++) {
	// 	for (int j = 1; j <= n; j++) {
	// 		cout << p1[i][j] << " \n"[j == n];
	// 	}
	// }

	// cout << "\n";
	// for (int i = 1; i <= n; i++) {
	// 	for (int j = 1; j <= n; j++) {
	// 		cout << p2[i][j] << " \n"[j == n];
	// 	}
	// }

	dp[0] = 0;
	for (int i = 1; i <= n; i++) {
		{
			int cost2 = get_p(p2, 1, i, 1, i);
			dp[i] = min(dp[i], cost2);
		}
		for (int j = 1; j < i; j++) {
			int cost1 = get_p(p1, j + 1, i, 1, j);
			int cost2 = get_p(p2, j + 1, i, j + 1, i);
			dp[i] = min(dp[i], cost1 + cost2 + dp[j]);
		}
	}
	cout << dp[n] << "\n";
}

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