ZOJ 1337 Pi

        题目稍微有点长,很多废话,题目的意思就是根据一个数论的定理求PI的近似值,定理如下:

 

        Given any pair of whole numbers chosen from a large, random collection of numbers, the probability that the two numbers have no common factor other than one (1) is 6/Pi^2.

 

        其实吧 ,我感觉这个定理挺神奇的,通过随即产生的数就求出pi的近似值;

        理解了题意,就好做了.

 

#include<stdio.h>int gcd(int a, int b){ return b==0?a:gcd(b, a%b);}int main(void){ int i,j,t,N; int Ncount,sum; int a[55]; while( scanf("%d",&N) && N != 0 ) { Ncount = sum = 0; for( i = 1 ; i <= N ; i++ ) scanf("%d",&a[i]); for( i = 1 ; i < N ; i++ ) for( j = i+1 ; j <= N ; j++) { t = a[i]>a[j]?gcd(a[i],a[j]):gcd(a[j],a[i]) ; if( t == 1 ) Ncount++; sum++; } //printf("%d %d",Ncount,sum); if(Ncount == 0) printf("No estimate for this data set./n"); else printf("%.6f/n",sqrt(6.0 * sum / Ncount)); } return 0;}