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【今日三题】素数回文(模拟) / 活动安排(区间贪心) / 合唱团(动态规划)

news 来源：原创 2025/5/13 22:13:46

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素数回文(模拟)

素数回文

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#include <iostream>
#include <string>
#include <cmath>
using namespace std;bool isprime(long long n)
{if (n < 2) return false;for (int i = 2; i <= sqrt(n); i++){if (n % i == 0) return false;}return true;
}
int main()
{string s;cin >> s;for (int i = s.size() - 2; i >= 0; i--) s += s[i];if (isprime(stoll(s))) cout << "prime" << endl;else cout << "noprime" << endl;return 0;
}

活动安排(区间贪心)

活动安排

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#include <iostream>
#include <algorithm>
using namespace std;const int N = 2e5 + 1;
using pii = pair<int, int>;
pii arr[N];
int n, a, b, res;int main() 
{cin >> n;for (int i = 0; i < n; i++){cin >> a >> b;arr[i].first = a;arr[i].second = b;}sort(arr, arr + n);int l = arr[0].first, r = arr[0].second;for (int i = 1; i < n; i++){int a = arr[i].first, b = arr[i].second;if (a >= r) res++;else b = min(b, r);l = a;r = b;}cout << res + 1 << endl;return 0;
}

合唱团(动态规划)

合唱团

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f[i][j]：从前i位同学中找j名同学，最后一个同学必选的最大能力值乘积；
g[i][j]：从前i位同学中找j名同学，最后一个同学必选的最小能力值乘积；

#include <iostream>
using namespace std;const long INF = 0x3f3f3f3f3f;
const int M = 55, N = 15;
long f[M][N], g[M][N];
long arr[M];
int n, a, k, d;
long res = -INF;int main() 
{cin >> n; for (int i = 1; i <= n; i++) cin >> arr[i];cin >> k >> d;for (int i = 1; i <= n; i++){f[i][1] = g[i][1] = arr[i];for (int j = 2; j <= min(i, k); j++){f[i][j] = -INF;g[i][j] = INF;for (int prev = max(i - d, j - 1); prev <= i - 1; prev++){f[i][j] = max(max(f[prev][j - 1] * arr[i], g[prev][j - 1] * arr[i]), f[i][j]);g[i][j] = min(min(f[prev][j - 1] * arr[i], g[prev][j - 1] * arr[i]), g[i][j]);}}}for (int i = k; i <= n; i++) res = max(res, f[i][k]);cout << res << endl;return 0;
}