sicily 1752 选择

最近一直都在做水题找自信中，嘿嘿....

 

// source code of submission 743067, Zhongshan University Online Judge System#include <iostream>#include <cstring>#include <algorithm>using namespace std;int prime(int a[],int n) //筛法素数产生器{ int i,j,k,x,num,*b; n++; n/=2; b=(int *)malloc(sizeof(int)*(n+1)*2); a[0]=2;a[1]=3;num=2; for(i=1;i<=2*n;i++) b[i]=0; for(i=3;i<=n;i+=3) for(j=0;j<2;j++) { x=2*(i+j)-1; while(b[x]==0) { a[num++]=x; for(k=x;k<=2*n;k+=x) b[k]=1; } } return num;}int binary_search(int a[],int n,int value) //二分查找函数{ int low = 0,high = n-1,mid; while(low <= high) //注意这里不要写成low < high { mid = low +(high-low)/2; if(a[mid] == value) return mid; if(a[mid] < value) low = mid+1; else high = mid-1; } return -1;}int main(){ int p[100000]; int n,i,w,res; n = prime(p,1000000); while(cin>>w,w!=-1) { res = binary_search(p,n,w); cout<<res+1<<endl; //数组从0开始计数，故输出应为res+1 } return 0;}