Codeforces Round #690 (Div. 3)
Codeforces Round #690 (Div. 3)
- A
#include<bits/stdc++.h>
using namespace std;
#pragma GCC optimize(2)
typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
void io(){ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);}
int t,n;
const int maxn=400;
int a[maxn],b[maxn];
int main()
{
io();
cin>>t;
while(t--){
cin>>n;
for(int i=1;i<=n;++i) cin>>a[i];
int tmp=(n+1)/2;
for(int i=1,j=1;i<=tmp;++i,j+=2){
b[j]=a[i];
}
for(int i=n,j=2;i>tmp;i--,j+=2){
b[j]=a[i];
}
for(int i=1;i<=n;++i) cout<<b[i]<<" ";
cout<<"\n";
}
return 0;
}
- B
#include<bits/stdc++.h>
using namespace std;
#pragma GCC optimize(2)
typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
void io(){ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);}
int t,n;
string s;
string p="2020";
int main()
{
io();
cin>>t;
while(t--){
cin>>n>>s;
int len=s.size();
int rec=n-4;
int f=0;
for(int i=0;i<len;++i){
string stmp=s;
stmp.erase(i,rec);
// cout<<stmp<<"\n";
if(stmp==p){
f=1;
// cout<<f<<"\n";
break;
}
}
if(f) cout<<"YES\n";
else cout<<"NO\n";
}
return 0;
}
- C
#include<bits/stdc++.h>
using namespace std;
#pragma GCC optimize(2)
typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
void io(){ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);}
int t,n;
int num[15];
int ans[15];
int f;
void dfs(int x,int pos,int rec)
{
if(x==0){
f=1;
return;
}
if(rec==0) return;
for(int i=1;i<=9;++i){
if(num[i]) continue;
// x-=i;
ans[pos]=i;
num[i]=1;
dfs(x-i,pos+1,rec-1);
if(f) break;
ans[pos]=0;
num[i]=0;
}
}
int main()
{
io();
cin>>t;
while(t--){
cin>>n;
if(n<10){
cout<<n<<"\n";
continue;
}
if(n>45){
cout<<-1<<"\n";
continue;
}
memset(num,0,sizeof(num));
memset(ans,0,sizeof(ans));
f=0;
for(int i=2;i<=9;++i){
dfs(n,0,i);
if(f) break;
}
if(f){
for(int i=0;ans[i]!=0;++i) cout<<ans[i];
cout<<"\n";
}else cout<<"-1\n";
}
return 0;
}
- D
#define _CRT_SECURE_NO_WARNINGS
#include<bits/stdc++.h>
using namespace std;
#pragma GCC optimize(2)
typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
void io() { ios::sync_with_stdio(false); cin.tie(0); cout.tie(0); }
const int maxn = 3010;
int t, n;
int a[maxn];
int main()
{
io();
cin >> t;
while (t--) {
cin >> n;
int maxx = 0, sum = 0;
for (int i = 1; i <= n; ++i) {
cin >> a[i];
sum += a[i];
maxx = max(maxx, a[i]);
}
int ans = 1e9;
for (int i = 1; i <= n; ++i) {
if (sum % i) continue;
if (sum / i < maxx) continue;
int tmp = sum / i;
int j = 1;
int tans = 0;
int f = 0;
for (int k = 0; k < i; ++k) {
int st = 0;
int recj = j;
for (; j <= n; ++j) {
st += a[j];
if (st == tmp) {
tans += (j - recj);
j++;
break;
}
if (st >= tmp) {
f = 1;
break;
}
}
if (k != i - 1 && j > n) f = 1;
if (f) break;
}
if(!f) ans = min(tans, ans);
}
cout << ans << "\n";
}
return 0;
}
-
E1 &E2
-
二分+组合数+逆元
- E1
#include <bits/stdc++.h>
using namespace std;
#pragma GCC optimize(2)
typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
void io()
{
ios::sync_with_stdio(false);
cin.tie(0);
cout.tie(0);
}
int t, n;
const int maxn = 2e5 + 10;
int a[maxn];
int main()
{
io();
cin >> t;
while (t--)
{
cin >> n;
for (int i = 0; i < n; ++i)
cin >> a[i];
sort(a, a + n);
long long ans = 0;
for (int i = 0; i < n - 2; ++i)
{
int tmp = a[i] + 2;
int pos = upper_bound(a, a + n, tmp) - a;
pos--;
if (pos >= i + 2)
{
ans += (1ll * (pos - i) * (1ll * (pos - i - 1)) / 2ll) * 1ll;
}
}
cout << ans << "\n";
}
return 0;
}
- E2
#include<bits/stdc++.h>
#define MOD 1000000007
using namespace std;
#pragma GCC optimize(2)
typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
void io(){ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);}
const int maxn=2e5+10;
int t,n,m,k;
int a[maxn];
ll ksm(ll x,ll y){ // 快速幂
ll ret=1;
x%=MOD;
while(y){
if(y&1)ret=ret*x%MOD;
x=(x%MOD)*(x%MOD);
x%=MOD;
y>>=1;
}
return ret;
}
ll jc(ll x){ // 算阶乘
ll rec=1;
while(x){
rec*=x;
rec%=MOD;
x-=1;
}
return rec;
}
int main()
{
io();
cin>>t;
while(t--){
cin>>n>>m>>k;
for(int i=0;i<n;++i) cin>>a[i];
sort(a,a+n);
long long ans=0;
for(int i=0;i<n-m+1;++i){
int tmp=a[i]+k;
int pos=upper_bound(a,a+n,tmp)-a; // 二分找范围
pos--;
ll w=jc(m-1);
ll inv=ksm(w,MOD-2); // 费马小定理
if(pos>=i+m-1){ // if里面都是计算组合数
ll rr=1;
for(int j=0;j<m-1;++j){
rr=(rr%MOD*(pos-i-j)%MOD+MOD)%MOD;
}
rr=(rr%MOD*inv%MOD+MOD)%MOD;
ans=(ans%MOD+rr%MOD)%MOD;
}
}
cout<<ans<<"\n";
}
return 0;
}
- F
- 二分+树状数组（差分建树）,树状数组很久没写过了，顺带复习一下（反正都是贴板子来着，主要是复习下差分建树（本来想手撸线段树，但是太懒了，线段树太长了
#include<bits/stdc++.h>
using namespace std;
#define mk(a, b) make_pair(a, b)
typedef pair<int, int> pii;
void io()
{
ios::sync_with_stdio(false);
cin.tie(0);
cout.tie(0);
}
const int maxn = 2e5 + 10;
int t, n;
pii pa[maxn];
int a[maxn];
int c[maxn];
int lowbit(int x) { return x & (-x); }
void updata(int pos, int k)
{
while (pos <= n) {
c[pos] += k;
pos += lowbit(pos);
}
}
int getsum(int pos)
{
int res = 0;
while (pos > 0) {
res += c[pos];
pos -= lowbit(pos);
}
return res;
}
int main()
{
io();
cin >> t;
while (t--) {
cin >> n;
for (int i = 1; i <= n; ++i) {
int a, b;
cin >> a >> b;
pa[i] = mk(a, b);
}
sort(pa + 1, pa + n + 1);
for (int i = 1; i <= n; ++i) a[i] = pa[i].first; // 懒人操作，懒得写cmp，所以直接把first单独存一下方便后面用upperbound，手写二分我容易出锅
memset(c, 0, (n + 5)*sizeof(int) );
int ans = 0;
for (int i = 1; i <= n; ++i) {
pii now = pa[i];
int y = now.second;
int pos = upper_bound(a, a + n + 1, y) - a - 1;
int tmp = getsum(i);
tmp += pos - i;
tmp++;
ans = max(ans, tmp);
updata(i, 1);
updata(pos + 1, -1);
}
cout << n - ans << "\n";
}
return 0;
}
- 最后纪念一下CF第一次看见比赛变绿
