Submission #823799

#	Time	Username	Problem	Language	Result	Execution time	Memory
823799		PoonYaPat	Boarding Passes (BOI22_passes)	C++14	60 / 100	2066 ms	1812 KiB

passes

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

ll ans,dp[1<<15]; //2 times expected value
int m,n,g[100005];
vector<int> group[15];

ll cal(ll a) {
    return a*(a-1)/2;
}

int main() {
    ios_base::sync_with_stdio(0); cin.tie(0);
    string s; cin>>s;
    n=s.size();
    for (int i=0; i<(1<<15); ++i) dp[i]=2e15;
    
    map<char,int> mp;
    for (int i=0; i<n; ++i) mp[s[i]]=0;
    for (auto k : mp) mp[k.first]=m++;
    for (int i=0; i<n; ++i) group[mp[s[i]]].push_back(i), g[i]=mp[s[i]];

    dp[0]=0;
    for (int mask=1; mask<(1<<m); ++mask) {
        //find dp[mask]
        bool have[15];
        for (int i=0; i<m; ++i) {
            if (mask&(1<<i)) have[i]=true;
            else have[i]=false;
        }

        for (int i=0; i<m; ++i) {
            if (mask&(1<<i)) { //consider case i is the last boarding group to put in

                ll cnt_back=0,sum_back=0,cnt_front=0,sum_front=0,cb=0,cf=0;
                for (int x=n-1; x>=0; --x) {
                    if (have[g[x]]) {
                        if (g[x]!=i) ++cnt_back;
                        else sum_back+=cnt_back, ++cb;
                    }
                }

                dp[mask]=min(dp[mask],dp[mask^(1<<i)]+cal(cb)+2*sum_back); //all get in from back

                for (int x=0; x<n; ++x) { //people number 0 to x get in from front
                    if (have[g[x]]) {
                        if (g[x]!=i) {
                            ++cnt_front;
                            --cnt_back;
                        } else {
                            ++cf;
                            --cb;
                            sum_front+=cnt_front;
                            sum_back-=cnt_back;
                            dp[mask]=min(dp[mask],dp[mask^(1<<i)]+cal(cf)+cal(cb)+2*sum_back+2*sum_front);
                        }
                    }
                }
            }
        }
    }

    cout<<dp[(1<<m)-1]/2;
    if (dp[(1<<m)-1]%2==1) cout<<".5";
}

• Subtask 1: 5 / 5
• Subtask 2: 25 / 25
• Subtask 3: 30 / 30
• Subtask 4: 0 / 40