CodeForces
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Simon has a prime number x and an array of non-negative integers a1, a2, ..., an.
Simon loves fractions very much. Today he wrote out number on a piece of paper. After Simon led all fractions to a common denominator and summed them up, he got a fraction: , where number t equals xa1 + a2 + ... + an. Now Simon wants to reduce the resulting fraction.
Help him, find the greatest common divisor of numbers s and t. As GCD can be rather large, print it as a remainder after dividing it by number 1000000007 (109 + 7).
The first line contains two positive integers n and x (1 ≤ n ≤ 105, 2 ≤ x ≤ 109) — the size of the array and the prime number.
The second line contains n space-separated integers a1, a2, ..., an (0 ≤ a1 ≤ a2 ≤ ... ≤ an ≤ 109).
Print a single number — the answer to the problem modulo 1000000007 (109 + 7).
2 22 2
8
3 31 2 3
27
2 229 29
73741817
4 50 0 0 0
1
In the first sample . Thus, the answer to the problem is 8.
In the second sample, . The answer to the problem is 27, as 351 = 13·27, 729 = 27·27.
In the third sample the answer to the problem is 1073741824 mod 1000000007 = 73741817.
In the fourth sample . Thus, the answer to the problem is 1.
题意是给你一个N位数,和一个素数X,求按公式相加后的最大公约数
引用以下这个博客里的话点击打开链接
分母的最终形式为x^s,s=a1+...+an;
每个分子为x^(s-ai);
如果出现相同分子,则cnt记录一下;
如果出现不同分子,但cnt可以整除x,则前面的幂数加一,i--,将变化后的值与后者相比较
最后用快速幂求分子是多少
#include <iostream>#include <iomanip>#include<stdio.h>#include<string.h>#include<stack>#include<stdlib.h>#include<queue>#include<map>#include<math.h>#include<algorithm>#include<vector>#define inf 1000000007#define LL long long int#define mem(a,b) memset(a,b,sizeof(a))using namespace std; LL a[100005];LL solve(LL x,LL m){ //快速幂 LL ans=1; x=x%inf; while(m) { if(m&1) ans=(ans*x)%inf; x=(x*x)%inf; m/=2; } return ans%inf;}int main(){ LL n,x; LL s=0; scanf("%lld%lld",&n,&x); for(int i=0;i<n;i++) { scanf("%lld",&a[i]); s+=a[i]; } for(int i=0;i<n;i++) { a[i]=s-a[i];//求出分子的幂数 } a[n]=-1; //sort排序幂数从小到大 sort(a,a+n); LL cnt=1,ans; for(int i=1;i<=n;i++) { if(a[i]!=a[i-1]) { //如果系数可以整除x,则在前者+1,前者值发生改变,i--再判断一次 if(cnt%x==0) { cnt/=x; a[i-1]+=1; i--; } else { //不相等,且系数不能整除x,即为所求 ans=a[i-1]; break; } } else //如果相等,记录加一 cnt++; } ans=min(ans,s); printf("%lld\n",solve(x,ans));}
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