66分求助

LHX_18460366315 @ 2024-02-12 14:10:26

#include<bits/stdc++.h>
using namespace std;
bool zhishu(long long x){
    if (x <= 1){
        return false;
    }
    for (long long i = 2;i <= sqrt(x);i++){
        if (x % i == 0){
            return false;
        }
    }
    return true;
}
bool hw(int n) {//判定回文，不懂请参考数字反转 
    int sum = 0;
    int k = n;
    while (n != 0) {
        sum =sum * 10 + n % 10;
        n /= 10;
    }
    if (sum == k){
        return true;
    }else{
        return false;
    }
}
bool weishu(int x){
    if((1000 <= x && x <= 9999) || (100000 <= x && x <= 999999)){
        return false;
    } 
    return true;
}
int main(){
    long long n,m;
    cin >> n >> m;
    if (n % 2 == 0){
        for (long long i = n + 1;i <= m;i += 2){
            if (zhishu(i) && hw(i) && weishu(i)){
                printf("%ld\n",i);
            }
        }
    }else{
        for (long long i = n;i <= m;i += 2){
            if (zhishu(i) && hw(i) && weishu(i)){
                printf("%ld\n",i);
            }
        }
    }
    return 0;
}

by Weekoder @ 2024-02-12 14:14:06

@ZZYX_18670145320 这题好像需要质数筛吧，你可以参考一下我的（埃氏筛）

#include <bits/stdc++.h>
using namespace std;
const int N = 1e7 + 5;
int a, b, prime[N + 5];
void getPrime() {
    for (int i = 2; i <= N; i++) {
        if (!prime[i]) prime[++prime[0]] = i;
        for (int j = 1; j <= N && i <= N / prime[j]; j++) {
            prime[prime[j] * i] = 1;
            if (i % prime[j] == 0) break;
        }
    }
}
bool ispalindrome(int n) {
    int sum = 0, nn = n;
    while (n) {
        sum *= 10;
        sum += n % 10;
        n /= 10;
    }
    if (nn == sum) return 1;
    return 0;
}
int main() {
    ios::sync_with_stdio(0);
    cin >> a >> b;
    getPrime();
    for (int i = 1; i <= N; i++) {
        if (prime[i] == 1 || prime[i] < a) continue;
        if (prime[i] > b) break;
        if (ispalindrome(prime[i]))
            cout << prime[i] << "\n";
    }
    return 0;
}

by Weekoder @ 2024-02-12 14:15:08

@ZZYX_18670145320 手滑打错了，是线性筛（欧拉筛）。

by LHX_18460366315 @ 2024-02-12 14:21:34

@Weekoder 谢谢