UVA 294 - Divisors

题目链接

题意：求一个区间内，因子最多的数字。
思路：由于区间保证最多1W个数字，因子可以遍历区间，然后利用事先筛出的素数求出质因子，之后因子个数为所有(质因子的个数+1)的积

代码：

#include 
   
     #include 
    
      #include 
     
       using namespace std; const int N = 35005; int prime[N], pn = 0, vis[N]; int t, a, b; int cal(int num) { int ans = 1; for (int i = 0; i < pn && prime[i] <= num; i++) { if (num % prime[i]) continue; int count = 1; while (num % prime[i] == 0) { count++; num /= prime[i]; } ans *= count; } return ans; } void solve() { int ans, Max = 0; for (int i = a; i <= b; i++) { if (Max < cal(i)) { ans = i; Max = cal(i); } } printf("Between %d and %d, %d has a maximum of %d divisors.\n", a, b, ans, Max); } int main() { for (int i = 2; i < N; i++) { if (vis[i]) continue; prime[pn++] = i; for (int j = i; j < N; j += i) vis[j] = 1; } scanf("%d", &t); while (t--) { scanf("%d%d", &a, &b); solve(); } return 0; }