題目連結
植樹表及質因數相關分解，請見
http://celinechiu0809.blogspot.tw/2015/04/c-sieve-mrthod.html
題目大意
給一個範圍L, U，不大於int範圍。U-L <= 10000
找出在這個範圍內擁有最多因數的數。
解題思路
先建質數表，後直因數分解
Code
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| #include <cstdlib>#include <cstdio>#include <cmath>using namespace std;int ans, divisor;bool is_prime[40000];void build_prime_tb(){ /*是質數:false, 不是質數:true*/ is_prime[0] = is_prime[1] = true; for (int i = 2; i <= sqrt(40000); i++) { if (!is_prime[i]) { for (int k=39999/i, j=i*k; k>=i; k--, j-=i) { if (!is_prime[k]) is_prime[j] = true; } } }}void prime_factor(int num){ /*質因數分解*/ int m = (int)(sqrt(num)+0.001); int x = num; int tmp=1, ppow; for (int i=2; i<=m; i++){ ppow = 0; if(!is_prime[i] && x%i==0){ ppow=0; while (x%i==0){ x /= i; ppow++; } tmp *= ppow+1; } } if (x>1) tmp *= 2; if (tmp > divisor) divisor=tmp, ans=num;}int main(){ int n; scanf("%d", &n); build_prime_tb(); while (n--){ int range_low, range_high; scanf("%d %d", &range_low, &range_high); ans = 0, divisor=0; for (int i=range_low; i<=range_high; i++) prime_factor(i); printf("Between %d and %d, %d has a maximum of %d divisors.\n", range_low, range_high, ans, divisor); } return 0;} |
