CF#315 C

来源：互联网发布：trpg跑团软件编辑：程序博客网时间：2024/05/01 15:14

#include <cstdio>#include <iostream>#include <algorithm>#include <queue>#include <cmath>#include <cstring>#include <stack>#include <set>#include <map>#include <vector>using namespace std;#define INF 0x2fffffff#define LL long long#define MAX(a,b) ((a)>(b))?(a):(b)#define MIN(a,b) ((a)<(b))?(a):(b)#define maxn 10000000int sum1[maxn];int is[maxn];int sum2[maxn];int fun(){    int t = sqrt(maxn);    is[0] = 1;    is[1] = 1;    for(int i = 0;i < t;i++){        if(!is[i]){            for(int j = i+i;j < maxn;j+=i){                is[j] = 1;             }        }    }    sum1[0] = 0;    for(int i = 1;i < maxn;i++){        sum1[i]=!is[i] + sum1[i-1];    }    sum2[0] = 0;    for(int i = 1;i < maxn;i++){        int cnt = 0;        int n = i;        int tmp = 0;        while(n){            tmp *= 10;            tmp += n%10;            n /= 10;            cnt++;        }        if(tmp == i){            sum2[i] = sum2[i-1] + 1;        }        else{            sum2[i] = sum2[i-1];        }    }}int main(){    fun();    LL p,q;    cin >> p >> q;    for(int i = maxn-1;i > 0;i--){        if(q*sum1[i] <= p * sum2[i]){            printf("%d\n",i);            break;        }     }    return 0;}

注意回文数的求法，和比较的时候从上开始，不能从下到上

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