UVA 294 - Divisors

题意：求一个区间内，因子最多的数字。

思路：因为区间保证最多1W个数字，因子能够遍历区间。然后利用事先筛出的素数求出质因子，之后因子个数为全部(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;}