P1820 寻找AP数

P1820 寻找AP数

这道题跟那个反素数挺像的，于是就使用了经典的打表。

打表程序：

#include<bits/stdc++.h>
using std::cin;
using std::cout;
using std::endl;
#define ll long long
const int primes[] = {0, 2, 3, 5, 7, 11, 13, 17, 19, 23, 29};// 10
const ll limit = 1500000000;
const ll INF = 0x3f3f3f3f3f3f3f3f;
ll maxv = -INF;
int ysgs(int x) {
    int ans = 1;
    for(int i = 1; i <= 10; i++) {
        int cnt = 0;
        while(x % primes[i] == 0) {
            cnt++; x /= primes[i];
        }
        ans = ans * (cnt + 1);
    }
    return ans;
}
int main() {
    freopen("out.txt", "w", stdout);
    printf("const int chart[] = {");
    for(int i = 1; i <= limit; i++) {
        ll temp = ysgs(i);
        if(temp > maxv) {
            printf("%d, ", i);
        }
        maxv = std::max(maxv, temp);
    }
    printf("};\n");
    return 0;
}

提交的程序：

#include<bits/stdc++.h>
using std::cin;
using std::cout;
using std::endl;
#define ll long long
const int chart[68] = {1, 2, 4, 6, 12, 24, 36, 48, 60, 120, 180, 240, 360, 720, 840, 1260, 1680, 2520, 5040, 7560, 10080, 15120, 20160, 25200, 27720, 45360, 50400, 55440, 83160, 110880, 166320, 221760, 277200, 332640, 498960, 554400, 665280, 720720, 1081080, 1441440, 2162160, 2882880, 3603600, 4324320, 6486480, 7207200, 8648640, 10810800, 14414400, 17297280, 21621600, 32432400, 36756720, 43243200, 61261200, 73513440, 110270160, 122522400, 147026880, 183783600, 245044800, 294053760, 367567200, 551350800, 698377680, 735134400, 1102701600, 1396755360};


int main() {
    ll n;
    while(cin >> n) {
        int idx = std::lower_bound(chart, chart + 68, n) - chart;
        if(chart[idx] > n) idx--;
        cout << chart[idx] << endl;
    }
    return 0;
}