HDU 5879 Cure（数学）

#include <cmath>
#include <vector>
#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
using namespace std;
typedef long long LL;
const double PI = acos(-1);
const double xxx = PI*PI/6.0;
double a[3000000];
char s[1000000];

int init(){
memset(a, 0, sizeof(a));
a[1] = 1.0;
int i;
for(i = 2; ; i++){
a[i] = a[i-1]+1.0/(1.0*i*i);
if(abs(a[i] - xxx) < 1e-6)
break;
}
return i;
}

int change(char *s){
int sum = 0;
for(int i = 0; i < strlen(s); i++){
sum = sum*10 + s[i]-'0';
}
return sum;
}

int judge(char *s){
int cnt = 0;
for(int i = 0; i < strlen(s); i++)
if(s[i] == '0') cnt++;
return strlen(s) - cnt;
}

int main(){
int k = init();
while(scanf("%s", s) != EOF){
if(s[0] == '-') continue;
int len = judge(s);
if(len == 0) continue;
if(len < 6) printf("%.5lf\n", a[change(s)]);
else printf("%.5lf\n", xxx);
}
return 0;
}