第十四届蓝桥杯c++b组题解

 

 这里用dfs写，带剪枝

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

const int N = 1e2 + 1;
int a[N];

set<int> s;

bool check(int date)
{
    int mm = date / 100 % 100;
    int dd = date % 100;
    if (mm < 1 || mm > 12)
        return false;
    if (mm == 1 || mm == 3 || mm == 5 || mm == 7 || mm == 8 || mm == 10 || mm == 12)
    {
        if (dd >= 1 && dd <= 31)
            return true;
    }
    else if (mm == 2)
    {
        if (dd >= 1 && dd <= 28)
            return true;
    }
    else if (dd >= 1 && dd <= 30)
        return true;

    return false;
}

void dfs(int x, int cnt, int date)
{
    if (x == 100)
        return;
    if (cnt == 8)
    {
        if (check(date))
            s.insert(date);
        return;
    }

    if (cnt == 0)
        date = 0;

    if ((cnt == 0 && a[x] == 2) || (cnt == 1 && a[x] == 0) || (cnt == 2 && a[x] == 2) || (cnt == 3 && a[x] == 3) || (cnt == 4 && a[x] >= 0 && a[x] <= 1) || (cnt == 5 && a[x] >= 0 && a[x] <= 9) || (cnt == 6 && a[x] >= 0 && a[x] <= 3) || (cnt == 7 & a[x] >= 0 && a[x] <= 9))
        dfs(x + 1, cnt + 1, date * 10 + a[x]); // 合法可以选

    dfs(x + 1, cnt, date); // 不选
}
int main()
{
    for (int i = 0; i < 100; i++)
        cin >> a[i];
    dfs(0, 0, 0);
    cout << s.size() << endl;

    return 0;
}

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

const int N = 23333333,M = N/2;
long double eps = 11625907.5798;
int cal(int i)
{
    long double p;
    long double n0 = i;
    long double n1 = N-i;
    p = -((n0*n0/N)*log2l(n0/N)+(n1*n1/N)*log2l(n1/N));
    //cout<<p<<endl;
    if(abs(p-eps)<0.0001)
        cout<<i<<endl;

    return p;
}

int main()
{
    //cout<<cal(114514)<<endl;
    for(int i = 1;i<=N/2;i++)
        cal(i);

    return 0;
}

 对答案使用二分,复杂度o(nlog(n))

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

const int N = 1e5 + 1;
int a[N], b[N], n;

bool checkmin(int mid)
{
    for (int i = 0; i < n; i++)
        if (a[i] / mid > b[i])
            return false;
    return true;
}

bool checkmax(int mid)
{
    for (int i = 0; i < n; i++)
        if (a[i] / mid < b[i])
            return false;
    return true;
}

int main()
{
    cin >> n;

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

    int l = 0, r = 1e9;
    while (l <= r)
    {
        int mid = (l + r) >> 1;
        if (checkmin(mid))
            r = mid - 1;
        else
            l = mid + 1;
    }

    cout << l << " ";

    l = 0, r = 1e9;
    while (l <= r)
    {
        int mid = (l + r) >> 1;
        if (checkmax(mid))
            l = mid + 1;
        else
            r = mid - 1;
    }

    cout << r << endl;

    return 0;
}

 

 

 

 

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

const int N = 1001;
int T, n;
int t[N], d[N], l[N];
bool st[N];
bool flag = false;

void dfs(int k, int time)
{
    if (k == n - 1)
    {
        flag = true;
        return;
    }

    for (int i = 0; i < n; i++)
    {
        if (!st[i])
        {
            if (t[i] + d[i] >= time)
            {
                st[i] = true;
                dfs(k + 1, max(time + l[i], t[i] + l[i]));
                st[i] = false; // 找完了放回去}
            }
        }
    }
}
void solve()
{
    flag = false;
    memset(st, 0, sizeof(st));
    cin >> n;
    for (int i = 0; i < n; i++)
        cin >> t[i] >> d[i] >> l[i];

    for (int i = 0; i < n; i++)
    {
        if (!st[i])
        {
            st[i] = true;
            dfs(0, t[i] + l[i]);
            st[i] = false;
        }
    }

    if (flag)
        cout << "YES" << endl;
    else
        cout << "NO" << endl;
}

int main()
{
    cin >> T;
    while (T--)
        solve();

    return 0;
}

/*
2
3
0 100 10
10 10 10
0 2 20
3
0 10 20
10 10 20
20 10 20

*/

 

 

dp

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

const int N = 1e5 + 1;

int f[N];
int a[N], last[N], st[N];
int n;

int get_the_first_number(int n)
{
    while (n)
    {
        int t = n % 10;
        n /= 10;
        if (n == 0)
            return t;
    }
    return 0;
}

int get_the_last_number(int n)
{
    return n % 10;
}

bool check(int a, int b)
{
    int a_last = get_the_last_number(a);
    int b_first = get_the_first_number(b);

    if(a_last==b_first)
        return true;
    return false;
}

int main()
{
    cin >> n;
    for (int i = 1; i <= n; i++)
        cin >> a[i];

    for (int i = 1; i <= n; i++)
    {
        f[i] = f[i - 1];
        st[i] = st[i - 1];
        if (i == 1 || check(st[i], a[i]))
        {
            f[i]++;
            st[i] = a[i];
        }
    }

    cout<<n-f[n]<<endl;

    return 0;
}