UVa 294 - Divisors

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通过这道题学到了2个知识：

1.一个数的质因子一定小于等于这个数的开根

2.一个数的因子（约数）数等于 π(各质因子数+1)

#include<cstdio>
#include<cstring>
#include<algorithm>
#include<cmath>
using namespace std;
const int maxn = 55555;
//#define DEBUG
int vis[maxn];
int prime[maxn];
int cnt = 0;
void GetPrime(){
    memset(vis,0,sizeof(vis));
    int m = sqrt(maxn) + 1;
    for(int i = 2; i < m; i++)if(!vis[i]){
        for(int j = i * i; j < maxn; j += i)
            vis[j] = 1;
    }
    for(int i = 2; i < maxn; i++)
        if(!vis[i]) prime[cnt++] = i;
    #ifdef DEBUG
    for(int i = 0; i < cnt; i++)
        printf("%d ",prime[i]);
    #endif // DEBUG
}
int solve(int n){
    int sum = 1;
    for(int i = 0; i < cnt && n > 1; i++){
        if(n % prime[i] == 0){
            int c = 1;
            while(n % prime[i] == 0){
                c ++;
                n /= prime[i];
            }
            sum *= c;
        }
    }
    return sum;
}
int main(){
    int n,T;
    GetPrime();
    scanf("%d",&T);
    while(T--){
        int a,b;
        scanf("%d%d",&a,&b);
        int temp = 0;
        int ret;
        for(int i = a; i <= b; i++){
            int e = solve(i);
            if(temp < e){
                temp = e;
                ret = i;
            }
        }
        printf("Between %d and %d, %d has a maximum of %d divisors.\n",a,b,ret,temp);
    }
    return 0;
}

UVa 294 - Divisors

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原文地址：http://blog.csdn.net/u013451221/article/details/44408637