Submission #936942

#	Time	Username	Problem	Language	Result	Execution time	Memory
936942		emanIaicepsa	Group Photo (JOI21_ho_t3)	C++14	100 / 100	476 ms	196700 KiB

Main

#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define dbg(...) cerr<<#__VA_ARGS__<<" = ";_do(__VA_ARGS__);
template<typename T> void _do(T x){cerr<<x<<"\n";}
template<typename T,typename ...U> void _do(T x,U ...y){cerr<<x<<", ";_do(y...);}



signed main(){
    ios::sync_with_stdio(0), cin.tie(0);
    int N;
    cin >> N;
    vector<int> arr(N + 1), pos(N + 1);
    for (int i = 1; i <= N; i++) cin >> arr[i], pos[arr[i]] = i; 
    vector<vector<int>> dp(N + 1, vector<int>(N + 1, 0));
    vector<vector<int>> psum(N + 1, vector<int>(N + 1, 0));

    dp[1][1] = 0;
    psum[1][pos[1]] = 1;
    for (int i = 1; i <= N; i++) psum[1][i] += psum[1][i - 1];


    
    auto inv = [&](int up, int val, int p) -> int {
        // how much >= val and position < p
        int cnt = 0, cnt2 = 0;
        cnt += psum[up][p] - psum[val - 1][p];
        // for (int i = val; i <= up; i++) {
        //     if (pos[i] < p) cnt2++;
        // }
        // dbg(up, val, cnt, cnt2);
        cnt += psum[val - 1][N] - psum[val - 1][p];
        // for (int i = 0; i < val; i++) {
        //     if (pos[i] > p) cnt2++;
        // }
        return cnt;
    };

    for (int i = 2; i <= N; i++) {
        dp[i][i] = 1e9;
        for (int j = 1; j < i; j++) {
            dp[i][j] = dp[i - 1][j] + inv(i - 1, j, pos[i]);
            dp[i][i] = min(dp[i][i], dp[i - 1][j] + inv(i - 1, i, pos[i]));
        }
        for (int j = 1; j <= i; j++) {
            psum[i][pos[j]]++;
        }
        for (int j = 1; j <= N; j++) {
            psum[i][j] += psum[i][j - 1];
            // dbg(i, j, psum[i][j]);
        }
    }

    int ans = 1e9;
    for (int i = 1; i <= N; i++) ans = min(ans, dp[N][i]);
    cout << ans << '\n';


}

Compilation message (stderr)

Main.cpp: In lambda function:
Main.cpp:27:22: warning: unused variable 'cnt2' [-Wunused-variable]
   27 |         int cnt = 0, cnt2 = 0;
      |                      ^~~~

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