abc360

A - A Healthy Breakfast

https://atcoder.jp/contests/abc360/tasks/abc360_a

https://atcoder.jp/contests/abc360/submissions/55049596

int main()
{
    string s;

    cin >> s;

    int ri, mi;

    for(int i=0; i<s.size(); i++){
        if (s[i] == 'R'){
            ri = i;
        } else if (s[i] == 'M'){
            mi = i;
        }
    }

    if (ri < mi){
        cout << "Yes" << endl;
    } else {
        cout << "No" << endl;
    }

    return 0;
}

 

B - Vertical Reading

https://atcoder.jp/contests/abc360/tasks/abc360_b

https://atcoder.jp/contests/abc360/submissions/55073344

string s, t;

int main()
{
    cin >> s >> t;

    int len = s.size();
    
    vector<char> cache[105];

    for(int w=1; w<=len-1; w++){
        for(int i=0; i<105; i++){
            cache[i].clear();
        }
        
        int iter = 0;
        while(iter < len){
            int row = iter/w;

            cache[row].push_back(s[iter]);
            
            iter++;
        }
        
        /*
        iterate every column
        */
        for(int i=0; i<w; i++){
            string res;
            
            /*
            iterate every row
            */
            for(int j=0; j<100; j++){
                if (i < cache[j].size()){
                    res += cache[j][i];
                } else {
                    break;
                }
            }
            
            if (res == t){
                cout << "Yes" << endl;
                return 0;
            }
        }
    }
    
    cout << "No" << endl;

    return 0;
}

 

C - Move It

https://atcoder.jp/contests/abc360/tasks/abc360_c

https://atcoder.jp/contests/abc360/submissions/55082543

typedef long long ll;

ll n;
ll a[100005];
ll w[100005];
map<ll, vector<ll>> buckets;


int main()
{
    cin >> n;
    
    for(int i=0; i<n; i++){
        cin >> a[i];
    }

    for(int i=0; i<n; i++){
        cin >> w[i];
    }

    for(int i=0; i<n; i++){
        int bucket_number = a[i];
        buckets[bucket_number].push_back(w[i]);
    }

    ll sum = 0;
    for(auto& one: buckets){
        vector<ll>& weights = one.second;
        sort(weights.begin(), weights.end());
        
        for(int i=0; i<weights.size()-1; i++){
            sum += weights[i];
        }
    }

    cout << sum << endl;

    return 0;
}

 

D - Ghost Ants

https://atcoder.jp/contests/abc360/tasks/abc360_d

https://atcoder.jp/contests/abc360/submissions/55099937

typedef long long ll;

ll n, t;
string s;
ll x[200005];

int main()
{
    cin >> n >> t;

    cin >> s;

    for(int i=0; i<n; i++){
        cin >> x[i];
    }

    vector<ll> positive, negative;

    for(int i=0; i<n; i++){
        if (s[i] == '1'){
            positive.push_back(x[i]);
        } else {
            negative.push_back(x[i]);
        }
    }

    sort(positive.begin(), positive.end());
    sort(negative.begin(), negative.end());

    ll cnt = 0;

    for(ll i=0; i<positive.size(); i++){
        vector<ll>::iterator range1, range2;

        range1 = upper_bound(negative.begin(), negative.end(), positive[i]);
        range2 = upper_bound(negative.begin(), negative.end(), positive[i]+2*t);
        
        ll diff = distance(range1, range2);
        
        cnt += diff;
    }

    cout << cnt << endl;

    return 0;
}

 

E - Random Swaps of Balls

https://atcoder.jp/contests/abc360/tasks/abc360_e

https://atcoder.jp/contests/abc360/submissions/55215609

typedef long long ll;

const ll m = 998244353;

ll fp(ll x, ll p){
    ll qp = x;
    ll ret = 1;
    
    while(p){
        if (p&1) ret = ret * qp % m;
        
        qp = qp * qp % m;
        
        p >>= 1;
    }
    
    return ret;
}

ll inv(ll x){
    return fp(x, m-2);
}

ll n, k;

int main()
{
    cin >> n >> k;
    
    ll invn = inv(n);
    ll invn1 = inv(n-1);
    /*
    state transfer after one swap action, 1 = first position, other = other n-1 position.
    src pos     -> dst pos        -      action probability to make this transfer
    1             -> 1            -   stay
    1             -> other        -   move
    other         -> other        -   stay
    other         -> 1            -   move/(n-1)
    */
    ll move = 2ll * (n-1) % m * invn % m * invn % m;
    ll stay = (1 - move + m) % m;
    ll move1 = move * invn1 % m;
    
    array<ll, 2> dp{};
    // in the begining, the black ball is on 1st position with 100% probability
    dp[0] = 1;
    
    for(ll i=0; i<k; i++){
        array<ll, 2> ndp{}; // new dp
        
        /*
        there are two status transfers to acquire dst pos == 1:
        1 -> 1
            suppose src pos is 1st, i.e. black ball is on 1st position
            action probability to keep dest pos == 1 is stay
        other -> 1
            suppose src pos is xth, x=2..n, i.e. black ball is on any other positions
            action probability to get dest pos == 1 is move1
        */
        ndp[0] = (1ll * dp[0] * stay % m + 1ll * dp[1] * move1 % m) % m;

        /*
        there are two status transfers to acquire dst pos == any of other positions:
        1 -> other
            suppose src pos is 1st, i.e. black ball is on 1st position
            action probability to keep dest pos == other is move
        other -> other
            suppose src pos is xth, x=2..n, i.e. black ball is on any other positions
            action probability to get dest pos == other is 1 - move1
        */
        ndp[1] = (1ll * dp[0] * move % m + 1ll * dp[1] * ((1 - move1 + m) % m) % m) % m;
        
//        dp.swap(ndp);
        dp = ndp;
    }
    
    /*
    get final probability
    */
    ll sum = (dp[0] + 1ll * (n + 2ll) % m * (n - 1ll) % m * inv(2) % m * dp[1] % m * invn1 % m) % m;
    
    cout << sum << endl;
    
    return 0;
}

 

reference:

https://www.cnblogs.com/Lanly/p/18277192#e---random-swaps-of-balls-abc360-e