HDU 5668 Circle （约瑟夫游戏，求解同余方程组）

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样例：

7 6 5 4 3 2 1

题解：约瑟夫环问题，可以转换成中国剩余定理，然后就是套模板了。好坑啊，我每轮游戏都从第一个人开始计数。。而且题意也理解错了。。输入是代表第一个人第七轮游戏才出局，而不是第七个人第一轮游戏出局。。。

#include <cstdio>#include <iostream>#include <cstring>#include <string>#include <cstdlib>#include <algorithm>#include <cmath>#include <vector>#include <set>#include <list>#include <queue>#include <map>#include <stack>using namespace std;#define L(i) i<<1#define R(i) i<<1|1#define INF  0x3f3f3f3f#define pi acos(-1.0)#define eps 1e-9#define maxn 100010#define MOD 1000000007int num[22],m[22],a[22],c[22];long long extend_gcd(long long a,long long b,long long &x,long long &y){    if(a == 0 && b == 0)        return -1;    if(!b)    {        x = 1;        y = 0;        return a;    }    long long d = extend_gcd(b,a%b,y,x);    y -= a/b*x;    return d;}bool solve(int &m0,int &a0,int m,int a){    long long y,x;    int g = extend_gcd(m0,m,x,y);    if(abs(a-a0)%g)        return 0;    x *= (a - a0) / g;    x %= m/g;    a0 = (x*m0 + a0);    m0 *= m/g;    a0 %= m0;    if(a0 < 0)        a0 += m0;    return 1;}bool MLSE(int &m0,int &a0,int n){    bool flag = 1;    m0 = 1;    a0 = 0;    for(int i = 0; i < n; i++)    if(!solve(m0,a0,m[i],a[i]))    {        flag = 0;        break;    }    return flag;}int main(){int t;scanf("%d",&t);while(t--){int n,flag[22];memset(flag,1,sizeof(flag));scanf("%d",&n);for(int i = 0; i < n; i++)            scanf("%d",&c[i]);        for(int i = 0; i < n; i++)            num[c[i]-1] = i+1;        int k = n,l = 1;        for(int i = 0; i < n; i++)        {            int o = 0;            for(int j = l; ; j++)            {                if(j > n)                    j -= n;                if(flag[j])                    o++;                if(j == num[i])                    break;            }            a[i] = o;            flag[num[i]] = 0;            l = num[i];            m[i] = k--;        }        int m0,a0;        if(MLSE(m0,a0,n))        {            if(!a0)                printf("%d\n",a0+m0);            else                printf("%d\n",a0);        }        else            printf("Creation August is a SB!\n");}}

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