Educational Codeforces Round 32

A.

#include <bits/stdc++.h>
#define PI acos(-1.0)
#define mem(a,b) memset((a),b,sizeof(a))
#define TS printf("!!!
")
#define pb push_back
#define inf 1e9
//std::ios::sync_with_stdio(false);
using namespace std;
//priority_queue<int,vector<int>,greater<int>> que;
const double EPS = 1.0e-8;
const double eps = 1.0e-8;
typedef pair<int, int> pairint;
typedef long long ll;
typedef unsigned long long ull;
const int maxn = 1e6 + 10;
const int  maxm = 300;
const int turn[4][2] = {{1, 0}, { -1, 0}, {0, 1}, {0, -1}};
//next_permutation
ll mod = 1e9 + 7;
int a[maxn];
int main()
{
        //freopen("out1.txt", "w", stdout);
        int anser = 0;
        int n;
        cin >> n;
        for (int i = 1; i <= n; i++)
        {
                cin >> a[i];
        }
        for (int i = 2; i < n; i++)
        {
                if (a[i] > a[i - 1] && a[i] > a[i + 1])
                {
                        anser++;
                }
                if (a[i] < a[i - 1] && a[i] < a[i + 1])
                {
                        anser++;
                }
        }
        cout << anser << endl;
}

B.

#include <bits/stdc++.h>
#define PI acos(-1.0)
#define mem(a,b) memset((a),b,sizeof(a))
#define TS printf("!!!
")
#define pb push_back
#define inf 1e9
//std::ios::sync_with_stdio(false);
using namespace std;
//priority_queue<int,vector<int>,greater<int>> que;
const double EPS = 1.0e-8;
const double eps = 1.0e-8;
typedef pair<int, int> pairint;
typedef long long ll;
typedef unsigned long long ull;
const int maxn = 1e6 + 10;
const int  maxm = 300;
const int turn[4][2] = {{1, 0}, { -1, 0}, {0, 1}, {0, -1}};
//next_permutation
ll mod = 1e9 + 7;
int num[maxn];
map<char, int> mp;
int main()
{
        //freopen("out1.txt", "w", stdout);
        int n;
        string a;
        cin >> n >> a;
        mp['L'] = 1, mp['R'] = 2, mp['U'] = 3, mp['D'] = 4;
        for (int i = 0; i < a.size(); i++)
        {
                num[mp[a[i]]]++;
        }
        cout << min(num[1], num[2]) * 2 + min(num[3], num[4]) * 2 << endl;
}

C.先把每个字母的dis算出来  然后取里面最小的

 dis[a[i] - 'a'] = max(dis[a[i] - 'a'], i - cur[a[i] - 'a']);

 ans = min(ans, dis[i]);

#include <bits/stdc++.h>
#define PI acos(-1.0)
#define mem(a,b) memset((a),b,sizeof(a))
#define TS printf("!!!
")
#define pb push_back
#define inf 1e9
//std::ios::sync_with_stdio(false);
using namespace std;
//priority_queue<int,vector<int>,greater<int>> que;
const double EPS = 1.0e-8;
const double eps = 1.0e-8;
typedef pair<int, int> pairint;
typedef long long ll;
typedef unsigned long long ull;
const int maxn = 1e6 + 10;
const int  maxm = 300;
const int turn[4][2] = {{1, 0}, { -1, 0}, {0, 1}, {0, -1}};
//next_permutation
ll mod = 1e9 + 7;
int cur[maxn];
int dis[maxn];
int main()
{
        //freopen("out1.txt", "w", stdout);
        int ans = INT_MAX;
        for (int i = 0; i <= 25; i++)
        {
                cur[i] = -1;
        }
        string a;
        cin >> a;
        int len = a.size();
        for (int i = 0; i < len; i++)
        {
                dis[a[i] - 'a'] = max(dis[a[i] - 'a'], i - cur[a[i] - 'a']);
                cur[a[i] - 'a'] = i;
        }
        for (int i = 0; i <= 25; i++)
        {
                if (dis[i] != 0)
                {
                        dis[i] = max(dis[i], len - cur[i]);
                        ans = min(ans, dis[i]);
                        //cout << dis[i] << endl;
                }
        }
        cout << ans << endl;
}

D.排列组合加错排

#include<bits/stdc++.h>
using namespace std;
int n,k;
long long ans;
long long C[1001][1001];
void calc_Cmn()//求组合数
{
    for(int i=0;i<1001;i++)
    {
        C[i][0]=C[i][i]=1;
        for(int j=1;j<i;j++) C[i][j]=C[i-1][j-1]+C[i-1][j];
    }
}
int main()
{
    calc_Cmn();
    cin>>n>>k;
    for(int i=n-1;i>=n-k;i--)
    {
        if(i==n-1) ans+=1;
        if(i==n-2) ans+=C[n][i];
        if(i==n-3) ans+=C[n][i]*2;
        if(i==n-4) ans+=C[n][i]*9;
    }
    cout<<ans<<endl;
}

E.折半搜索

#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define pb push_back
#define mem(a,b) memset(a,b,sizeof(a)) 

const int N=50;
int a[N];
set<int>s; 
int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);
    int n,m;
    cin>>n>>m;
    for(int i=0;i<n;i++)cin>>a[i],a[i]=a[i]%m;
    sort(a,a+n);
    int hf=n/2;
    int _hf=n-hf;
    for(int i=0;i<(1<<hf);i++)
    {
        int t=0;
        for(int j=0;j<hf;j++)if((1<<j)&i)t=(t+a[j])%m;
        s.insert(t);
    }
    set<int>::iterator it;
    int ans=0;
    for(int i=0;i<(1<<_hf);i++)
    {
        int t=0;
        for(int j=0;j<_hf;j++)if((1<<j)&i)t=(t+a[j+hf])%m;
        it=s.upper_bound(m-1-t);
        if(it==s.begin())
        {
            ans=max(ans,t);
            continue;
        }
        it--;
        ans=max(ans,t+*it);
    }
    cout<<ans<<endl;
    return 0;
}