uva 10277 Boastin' Red Socks

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红袜子数a 总袜子数b

a*(a - 1)/b*(b-1) = p/q

因为要b最小，所以从2-50000枚举b 二分查找a

注意概率为0和1的情况。

#include <iostream>#include<stdio.h>using namespace std;unsigned long long p,q,d,tmp,tmp1;unsigned long long low,high,mid,i;unsigned long long gcd(unsigned long long p,unsigned long long q){    return q == 0?p:gcd(q,p%q);}int main(){    while(scanf("%llu %llu",&p,&q),p+q)    {        if(p==q)        {            printf("2 0\n");            continue;        }        if(p==0) {printf("0 2\n");continue;}        d = gcd(p,q);        p/=d;        q/=d;        int ok = 0;        for(i = 2; i<=50000; i++)        {            low = 2;            high = i;            tmp = p*i*i-p*i;            while(low <= high)            {                mid = (low+high)>>1;                tmp1 = mid*mid*q-mid*q;                if(tmp1<tmp) low = mid+1;                else if(tmp1 > tmp) high = mid-1;                else { printf("%llu %llu\n",mid,i-mid);ok = 1;break;}            }            if(ok) break;        }        if(!ok) printf("impossible\n");    }    return 0;}

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