hdu 1041 (OO approach, private constructor to prevent instantiation, sprintf) 分类： hdoj 2015-06-17 15:57 25人阅读 评论(0) 收藏

a problem where OO seems more natural to me, implementing a utility class not instantiable.

how to prevent instantiation, thanks to http://stackoverflow.com/questions/10558393/prevent-instantiation-of-an-object-outside-its-factory-method/10558404#10558404

#include <cstdio>
#include <algorithm>
class CompTrans {
    CompTrans() { }
    static const unsigned NUMS_LEN=240000, MAX_NUM=1000, BASE=1000000000;
    static bool isinitialized;
    static char nums[NUMS_LEN];
    static char* pos[MAX_NUM+2];
public:
    static bool isinited() { return isinitialized; }
    static void init();
    static void printnth(unsigned n) { puts(pos[n]); }
    static unsigned getMAX_NUM() { return MAX_NUM; }
};
bool CompTrans::isinitialized=false;
char CompTrans::nums[];
char* CompTrans::pos[];
void CompTrans::init() {
    if(isinited()) return;
    int i,j,k;
    char *p=nums;
    const int NSIZE=40;
    unsigned n1[NSIZE]={0}, n2[NSIZE]={1}, n3[NSIZE]={0},tmp, *p1,*p2,*p3,*ptmp, carry;
    p1=n1,p2=n2,p3=n3;
    for(k=0, i=1;i<=MAX_NUM;++i) {
        pos[i]=p;
        p+=sprintf(p,"%u",p1[k]);
        for(j=k-1;j>=0;--j) p+=sprintf(p,"%09u",p1[j]);
        *p++=0;
        if(p2[k+1]!=0) ++k;
        for(carry=0, j=0;j<=k;++j) {
            tmp=carry+p2[j]+(p1[j]<<1);
            carry=tmp/BASE;
            p3[j]=tmp%BASE;
        }
        p3[j]=carry;
        ptmp=p1; p1=p2; p2=p3; p3=ptmp;
    }
    isinitialized=true;
}
int main() {
    //freopen("input.txt","r",stdin);
    int n;
    if(!CompTrans::isinited()) CompTrans::init();
    while(scanf("%d",&n)!=EOF && n<=CompTrans::getMAX_NUM()) {
        CompTrans::printnth(n);
    }
    return 0;
}

版权声明：本文为博主原创文章，未经博主允许不得转载。// p.s. If in any way improment can be achieved, better performance or whatever, it will be well-appreciated to let me know, thanks in advance.