【模板】baby_step giant_step poj 2417
2016-09-16 11:18
344 查看
baby_step giant_step模板:
求同余式a^(L)=b(mod p)中L的解,令L=i*m-j(m=sqrt(n)),则原式表示为a^(i*m)=b*a^j (mod p),将a^j的值存入hash表中,枚举i,若表中存在a^(i*m)的值,则存在a^L=b(mod p)即有解。模板:(摘自http://www.kuangbin.org/)
/*** //baby_step giant_step // a^x = b (mod n) n是素数和不是素数都可以 //转化成a^(i*m-j)=b(mod n)求解 // 求解上式 0<=x < n的解 初始化head ***/ #define MOD 76543 int hs[MOD],head[MOD],next[MOD],id[MOD],top; void insert(int x,int y) { int k = x%MOD; hs[top] = x, id[top] = y, next[top] = head[k], head[k] = top++; } int find(int x) { int k = x%MOD; for(int i = head[k]; i != -1; i = next[i]) if(hs[i] == x) return id[i]; return -1; } int BSGS(int a,int b,int n) { memset(head,-1,sizeof(head)); top = 1; if(b == 1)return 0; int m = sqrt(n*1.0), j; long long x = 1, p = 1; for(int i = 0; i < m; ++i, p = p*a%n)insert(p*b%n,i); for(long long i = m; ; i += m) { if( (j = find(x = x*p%n)) != -1 )return i-j; if(i > n)break; } return -1; } int n,b,p; int main() { while(~scanf("%d%d%d",&p,&b,&n)) { memset(head,-1,sizeof head); int ans=BSGS(b,n,p); if(ans==-1) puts("no solution"); else printf("%d\n",ans); } return 0; }
相关文章推荐
- poj 2417 Discrete Logging 求解模方程a^x=b(mod n),n为素数+模板题(baby_step giant_step)
- 邝斌的ACM模板(Baby-Step Giant-Step)
- hdu 2815 Mod Tree 模方程a^x=b(mod n),n为任意正整数+模板题(扩展Baby Step Giant Step)
- poj 2417 baby_step giant_step 高次同余方程
- POJ 2417 baby_step giant_step 小步大步算法 a^x == b(mod n) 求解0<=x<n的值
- poj 2417 && poj3243(Baby-Step Giant-Step)
- POJ 2417 Discrete Logging (Baby-Step Giant-Step)
- poj 2417 && poj3243(Baby-Step Giant-Step)
- Poj 2417 Discrete Logging (Baby Step Giant Step 解 a^x = b (mod n) n为素数)
- poj_2417 (baby_step,giant_step算法)
- 高次同余方程:poj 3243+poj 2417+hdu 2815 (Baby Step Giant Step 算法)
- POJ 2417 Discrete Logging(高次同余方程-Baby-Step,Giant-Step)
- 2417 Discrete Logging 计算最小的x使得a^x=b(mod n) n是素数 Baby_step_Giant_step
- POJ - 2417 Discrete Logging(Baby-Step Giant-Step)
- POJ 2417:Discrete Logging——Baby Step, Giant Step
- POJ 2417 Discrete Logging ( Baby step giant step )
- POJ 2417 Discrete Logging (Baby Step Giant Step算法)
- poj 2417 Discrete Logging 数论baby_step,giant_step算法
- POJ 2417 Discrete Logging (baby_step,giant_step算法)
- 【poj3243-Clever Y】高次同余方程-拓展BabyStepGiantStep