HDU 6623 Minimal Power of Prime(思维)题解

题意:

已知任意大于\(1\)的整数\(a = p_1^{q_1}p_2^{q_2} \cdots p_k^{q_k}\),现给出\(a \in [2,1e18]\),求\(min\{q_i\},q \in [1, k]\)。即求质因数分解后,最小指数是多少。

思路:

因为\(a \in [2,1e18]\),所以我们现打一个\(1e4\)以内的质数表,然后直接求出\(1e4\)以内的情况。
上面弄完了,那么现在最多只有\(4\)个质因子,情况如下:
\(n = p^4\),这种情况就是\(4\)
\(n = p^3\),这种情况是3次,\(n = p_1^3p_2\)就直接和最后一种答案一样
\(n = p^2\)\(p = p_1 * p_1\)就是第一种情况
\(n = p\)

代码:

#include<map>
#include<set>
#include<cmath>
#include<cstdio>
#include<stack>
#include<ctime>
#include<vector>
#include<queue>
#include<cstring>
#include<string>
#include<sstream>
#include<iostream>
#include<algorithm>
typedef long long ll;
using namespace std;
const int maxn = 10000 + 5;
const int INF = 0x3f3f3f3f;
const ll MOD = 1e9 + 7;
using namespace std;
int prime[maxn], p[maxn], cnt;
void init(){
    memset(p, 0, sizeof(p));
    cnt = 0;
    for(int i = 2; i < maxn; i++){
        if(!p[i]){
            prime[cnt++] = i;
        }
        for(int j = 0; j < cnt && i * prime[j] < maxn; j++){
            p[i * prime[j]] = 1;
            if(i % prime[j] == 0) break;
        }
    }
}
bool triple(ll n){
    ll l = 1e4, r = 1e6;
    while(l <= r){
        ll m = (l + r) >> 1;
        ll ret = m * m * m;
        if(ret == n) return true;
        if(ret > n) r = m - 1;
        else l = m + 1;
    }
    return false;
}
int main(){
    int T;
    init();
    scanf("%d", &T);
    while(T--){
        ll n;
        scanf("%lld", &n);
        int ans = 1000;
        for(int i = 0; i < cnt && prime[i] <= n; i++){
            if(n % prime[i] == 0){
                int num = 0;
                while(n % prime[i] == 0){
                    num++;
                    n /= prime[i];
                }
                ans = min(ans, num);
            }
        }

        if(n > 1 && ans > 1){
           ll t1 = ll(sqrt(n));
           ll t2 = ll(sqrt(t1));
           if(t2 * t2 * t2 * t2 == n) ans = min(ans, 4);
           else if(t1 * t1 == n) ans = min(ans, 2);
           else if(triple(n)) ans = min(ans, 3);
           else ans = 1;
        }
        printf("%d\n", ans);

    }
    return 0;
}

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转载自www.cnblogs.com/KirinSB/p/11290778.html
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