Educational Codeforces Round 39

Educational Codeforces Round 39 

D. Timetable

令(dp[i][j])表示前(i)天逃课了(j)节课的情况下，在学校的最少时间

转移就是枚举第(i)天逃了(x)节课，然后取当天逃(x)节课情况下在学校的最小值即可

view code

#pragma GCC optimize("O3")
#pragma GCC optimize("Ofast,no-stack-protector")
#include<bits/stdc++.h>
using namespace std;
#define INF 0x3f3f3f3f
#define endl "
"
#define LL long long int
#define vi vector<int>
#define vl vector<LL>
#define all(V) V.begin(),V.end()
#define sci(x) scanf("%d",&x)
#define scl(x) scanf("%lld",&x)
#define scs(s) scanf("%s",s)
#define pii pair<int,int>
#define pll pair<LL,LL>
#ifndef ONLINE_JUDGE
#define cout cerr
#endif
#define cmax(a,b) ((a) = (a) > (b) ? (a) : (b))
#define cmin(a,b) ((a) = (a) < (b) ? (a) : (b))
#define debug(x)  cerr << #x << " = " << x << endl
function<void(void)> ____ = [](){ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0);};
template <typename T> vector<T>& operator << (vector<T> &__container, T x){ __container.push_back(x); return __container; }
template <typename T> ostream& operator << (ostream &out, vector<T> &__container){ for(T _ : __container) out << _ << ' '; return out; }
const int MAXN = 2e5+7;
int n, m, k;
char s[MAXN];
void solve(){
    sci(n); sci(m); sci(k);
    vi f(k+1,n*m);
    f[k] = 0;
    for(int d = 1; d <= n; d++){
        vi next_f(k+1,n*m);
        scs(s+1);
        vi A; for(int i = 1; i <= m; i++) if(s[i]=='1') A << i;
        vi cost(A.size()+1,n*m);
        for(int i = 0; i <= A.size(); i++){
            if(i==A.size()) cost[i] = 0;
            else for(int j = 0; j <= i; j++) cmin(cost[i],A[A.size() - 1 - i + j] - A[j] + 1);
        }
        for(int pre = 0; pre <= k; pre++) for(int cur = 0; cur <= min(pre,(int)A.size()); cur++) cmin(next_f[pre-cur],f[pre]+cost[cur]);
        f.swap(next_f);
    }
    cout << *min_element(all(f)) << endl;
}
int main(){
    #ifndef ONLINE_JUDGE
    freopen("Local.in","r",stdin);
    freopen("ans.out","w",stdout);
    #endif
    solve();
    return 0;
}

E.  Largest Beautiful Number

考虑从后往前枚举每个位置，判断在这个位置之前全部相同，这个位置比原来小的情况下是否存在合法解即可

特判长度为奇数的情况和小于等于(1xxxxxx1)的情况

view code

#pragma GCC optimize("O3")
#pragma GCC optimize("Ofast,no-stack-protector")
#include<bits/stdc++.h>
using namespace std;
#define INF 0x3f3f3f3f
#define endl "
"
#define LL long long int
#define vi vector<int>
#define vl vector<LL>
#define all(V) V.begin(),V.end()
#define sci(x) scanf("%d",&x)
#define scl(x) scanf("%lld",&x)
#define scs(s) scanf("%s",s)
#define pii pair<int,int>
#define pll pair<LL,LL>
#ifndef ONLINE_JUDGE
#define cout cerr
#endif
#define cmax(a,b) ((a) = (a) > (b) ? (a) : (b))
#define cmin(a,b) ((a) = (a) < (b) ? (a) : (b))
#define debug(x)  cerr << #x << " = " << x << endl
function<void(void)> ____ = [](){ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0);};
template <typename T> vector<T>& operator << (vector<T> &__container, T x){ __container.push_back(x); return __container; }
template <typename T> ostream& operator << (ostream &out, vector<T> &__container){ for(T _ : __container) out << _ << ' '; return out; }
const int MAXN = 2e5+7;
int n;
string s;
void solve(){
    cin >> s;
    function<bool(void)>check = [&](){
        string str(s.size(),'0');
        str.front() = str.back() = '1';
        return str >= s;
    };
    if(s.size()&1 or check()){
        for(int i = 1; i <= (s.size()&1 ? s.size() - 1 : s.size() - 2); i++) cout << 9;
        cout << endl; return;
    }
    vi cnt(10,0);
    for(int i = 0; i < s.size(); i++) cnt[s[i]-'0'] ^= 1;
    for(int i = s.size() - 1; ~i; i--){
        cnt[s[i]-'0'] ^= 1;
        for(char c = s[i] - 1; c >= '0'; c--){
            cnt[c-'0'] ^= 1;
            int tot = accumulate(all(cnt),0);
            if(tot>s.size()-i-1){
                cnt[c-'0'] ^= 1;
                continue;
            }
            string str(s);
            s[i] = c;
            int cur = i;
            for(int j = 0; j < s.size()-i-1-tot; j++) s[++cur] = '9';
            for(int j = 9; ~j; j--) if(cnt[j]) s[++cur] = j + '0';
            cout << s << endl;
            return;
        }
    }
}
int main(){
    #ifndef ONLINE_JUDGE
    freopen("Local.in","r",stdin);
    freopen("ans.out","w",stdout);
    #endif
    int tt; for(cin >> tt; tt--; solve());
    return 0;
}

F. Fibonacci String Subsequences

(dp[i][l][r])表示(f(i))中子串(s[l:r])以子序列的方式出现的次数，考虑转移

对于一般情况，可以考虑把(s[l:r])分成(s[l:k])和(s[k+1:r])，然后分别在(f(i-1))和(f(i-2))中找

其次考虑(s[l:r])全在(f(i-1))或(f(i-2))中，如果(r=n-1)，那么在(f(i-1)中找到)(s[l:r])出现次数之后由于后面可以随便选，乘上(2^{fib(i-2)})即可，否则只算左边一部分，对于(l=0)的情况类似处理即可

view code

#pragma GCC optimize("O3")
#pragma GCC optimize("Ofast,no-stack-protector")
#include<bits/stdc++.h>
using namespace std;
#define INF 0x3f3f3f3f
#define endl "
"
#define LL long long int
#define vi vector<int>
#define vl vector<LL>
#define all(V) V.begin(),V.end()
#define sci(x) scanf("%d",&x)
#define scl(x) scanf("%lld",&x)
#define scs(s) scanf("%s",s)
#define pii pair<int,int>
#define pll pair<LL,LL>
#ifndef ONLINE_JUDGE
#define cout cerr
#endif
#define cmax(a,b) ((a) = (a) > (b) ? (a) : (b))
#define cmin(a,b) ((a) = (a) < (b) ? (a) : (b))
#define debug(x)  cerr << #x << " = " << x << endl
function<void(void)> ____ = [](){ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0);};
template <typename T> vector<T>& operator << (vector<T> &__container, T x){ __container.push_back(x); return __container; }
template <typename T> ostream& operator << (ostream &out, vector<T> &__container){ for(T _ : __container) out << _ << ' '; return out; }
const int MAXN = 2e2+7;
const int MOD = 1e9+7;
LL ksm(LL a, LL b){
    LL ret = 1;
    while(b){
        if(b&1) ret = ret * a % MOD;
        b >>= 1;
        a = a * a % MOD;
    }
    return ret;
}
int n, x, fib[MAXN], f[MAXN][MAXN][MAXN];
string s;
int dp(int x, int l, int r){
    int &ret = f[x][l][r];
    if(~ret) return ret;
    if(x==0) return (ret = ((l==r) and s[l]=='0'));
    if(x==1) return (ret = ((l==r) and s[l]=='1'));
    ret = 0;
    if(r==n-1) ret = (ret + 1ll * dp(x-1,l,r) * ksm(2,fib[x-2])) % MOD;
    else ret = (ret + 1ll * dp(x-1,l,r)) % MOD;
    if(l==0) ret = (ret + 1ll * dp(x-2,l,r) * ksm(2,fib[x-1])) % MOD;
    else ret = (ret + 1ll * dp(x-2,l,r)) % MOD;
    for(int i = l; i < r; i++) ret = (ret + 1ll * dp(x-1,l,i) * dp(x-2,i+1,r)) % MOD;
    return ret;
}
void solve(){
    cin >> n >> x >> s;
    fib[0] = fib[1] = 1;
    for(int i = 2; i < MAXN; i++) fib[i] = (fib[i-1] + fib[i-2]) % (MOD - 1);
    memset(f,255,sizeof(f));
    cout << dp(x,0,n-1) << endl;
}
int main(){
    #ifndef ONLINE_JUDGE
    freopen("Local.in","r",stdin);
    freopen("ans.out","w",stdout);
    #endif
    solve();
    return 0;
}

G. Almost Increasing Array

假设没有删一个数的条件的话，就是把原序列(A)中的所有(A[i])变成(A[i]-i)，然后算最长非降子序列

现在考虑枚举删掉的数为(A[k])，那么对于(k)之前的数(A[i])来说，需要减去(i)，对于(k)之后的数(A[j])来说，需要减去(j-1)

那么之需要知道以(k-1)为结尾的最长非降子序列的长度和大于(k)的部分中起始值大于等于(A[k-1])的最长非降子序列即可

那么可以用线段树来维护

view code

#pragma GCC optimize("O3")
#pragma GCC optimize("Ofast,no-stack-protector")
#include<bits/stdc++.h>
using namespace std;
#define INF 0x3f3f3f3f
#define endl "
"
#define LL long long int
#define vi vector<int>
#define vl vector<LL>
#define all(V) V.begin(),V.end()
#define sci(x) scanf("%d",&x)
#define scl(x) scanf("%lld",&x)
#define scs(s) scanf("%s",s)
#define pii pair<int,int>
#define pll pair<LL,LL>
#ifndef ONLINE_JUDGE
#define cout cerr
#endif
#define cmax(a,b) ((a) = (a) > (b) ? (a) : (b))
#define cmin(a,b) ((a) = (a) < (b) ? (a) : (b))
#define debug(x)  cerr << #x << " = " << x << endl
function<void(void)> ____ = [](){ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0);};
template <typename T> vector<T>& operator << (vector<T> &__container, T x){ __container.push_back(x); return __container; }
template <typename T> ostream& operator << (ostream &out, vector<T> &__container){ for(T _ : __container) out << _ << ' '; return out; }
const int MAXN = 4e5+7;
int n, A[MAXN];
struct SegmentTree{
    int l[MAXN<<2], r[MAXN<<2], maxx[MAXN<<2];
    #define ls(rt) rt << 1
    #define rs(rt) rt << 1 | 1
    #define pushup(rt) maxx[rt] = max(maxx[ls(rt)],maxx[rs(rt)])
    void build(int L, int R, int rt = 1){
        l[rt] = L; r[rt] = R;
        maxx[rt] = 0;
        if(L+1==R) return;
        int mid = (L + R) >> 1;
        build(L,mid,ls(rt)); build(mid,R,rs(rt));
    }
    void modify(int pos, int x, int rt = 1){
        if(l[rt] + 1 == r[rt]){
            maxx[rt] = x;
            return;
        }
        int mid = (l[rt] + r[rt]) >> 1;
        if(pos<mid) modify(pos,x,ls(rt));
        else modify(pos,x,rs(rt));
        pushup(rt);
    }
    int qmax(int L, int R, int rt = 1){
        if(L>=r[rt] or l[rt]>=R) return 0;
        if(L<=l[rt] and r[rt]<=R) return maxx[rt];
        return max(qmax(L,R,ls(rt)),qmax(L,R,rs(rt)));
    }
}ST;
int f[MAXN];
void solve(){
    sci(n);
    vi vec;
    for(int i = 1; i <= n; i++) sci(A[i]), A[i] -= i, vec << A[i] << A[i] + 1;
    sort(all(vec)); vec.erase(unique(all(vec)),vec.end());
    auto ID = [&](int x){ return lower_bound(all(vec),x) - vec.begin() + 1; };
    ST.build(0,vec.size()+1);
    for(int i = 1; i <= n; i++){
        int x = ID(A[i]);
        f[i] = ST.qmax(0,x+1) + 1;
        ST.modify(x,f[i]);
    }
    int ret = f[n-1];
    ST.build(0,vec.size()+1);
    for(int i = n; i >= 2; i--){
        ret = max(ret,f[i-1]+ST.qmax(ID(A[i-1]),vec.size()+1));
        int x = ID(A[i]+1);
        ST.modify(x,ST.qmax(x,vec.size()+1)+1);
    }
    cmax(ret,ST.qmax(0,vec.size()+1));
    cout << n - 1 - ret << endl;
}
int main(){
    #ifndef ONLINE_JUDGE
    freopen("Local.in","r",stdin);
    freopen("ans.out","w",stdout);
    #endif
    solve();
    return 0;
}