poj 2369 Permutations 置换水题

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找循环节求lcm就够了，若答案是12345应该输出1，被坑了下。

#include<iostream>#include<cstdio>#include<cstring>#include<string>#include<algorithm>#include<cmath>using namespace std;#define INF 0x3FFFFFF#define MAXN 2222#define eps 1e-6int a[MAXN],p[MAXN],b[MAXN],vis[MAXN];int gcd(int a,int b) {return a%b==0?b:gcd(b,a%b);}int lcm(int a,int b) {return a/gcd(a,b)*b;}int main(){    int n;    while(~scanf("%d",&n))    {        for(int i=1;i<=n;i++)        {            a[i]=i;            vis[i]=0;            scanf("%d",&p[i]);        }        int ans=1;        for(int i=1;i<=n;i++)        {            if(vis[i]) continue;            int now=a[i];            int cnt=0;            while(1)            {                vis[now]=1;                now=p[now];                cnt++;                if(now==a[i]) break;            }            ans=lcm(ans,cnt);        }        printf("%d\n",ans);    }    return 0;}

4 0