Bestcoder round # 7-A, B, c

A: Little Pony and Permutation

Direct brute force search, complexity O (N)

#include<stdio.h>#include<iostream>#include<stdlib.h>#include<string.h>#include<algorithm>#include<vector>#include<math.h>#include<queue>#include<stack>#include<map>#pragma comment(linker, "/STACK:1024000000,1024000000")using namespace std;#define maxn 110000int a[maxn];int vis[maxn];int main(){    int n;    while(~scanf("%d",&n))    {        for(int i=1;i<=n;i++)scanf("%d",&a[i]);        memset(vis,0,sizeof(vis));        for(int i=1;i<=n;i++)        {            if(vis[i])continue;            int x=i;            cout<<"("<<x;            vis[x]=1;            x=a[x];            while(!vis[x])            {                vis[x]=1;                cout<<" "<<x;                x=a[x];            }            cout<<")";        }        cout<<endl;    }    return 0;}

B: Little Pony and Alohomora Part I

We can find that this is a harmonic sequence.

Then... That's all .. ,

#include<stdio.h>#include<iostream>#include<stdlib.h>#include<string.h>#include<algorithm>#include<vector>#include<math.h>#include<queue>#include<stack>#include<map>#pragma comment(linker, "/STACK:1024000000,1024000000")using namespace std;#define maxn 1100000double f[maxn];int main(){    int n;    f[1]=1.0;    for(int i=2;i<maxn;i++)f[i]=f[i-1]+1.0/i;    while(~scanf("%d",&n))    {        if(n<maxn)printf("%.4lf\n",f[n]);        else printf("%.4lf\n",log(n)+0.5772156649);    }    return 0;}

C: Little Pony and dice

DP [I]: probability of just going to point I

DP [I] = DP [I-1] * (1/m) + (DP [I-1]-DP [i-m-1] * (1.0/m ))

DP [I-1] * (1/m) represents the probability of moving from the point of I-1 to the point of I.

(DP [I-1]-DP [i-m-1] * (1.0/m) All points that walk to the I-1 can go to I, and the probability of going to I-1 is the same as that of going to I.

If the difference between two adjacent I dp [I] is very small, the change of the next DP [I] is also very small. This value will be used in the future. Therefore, direct output is good.

<pre name="code" class="cpp">#include<iostream>#include<stdio.h>#include<string.h>#include<algorithm>#include<iostream>#include<vector>#include<set>#include<string>#include<math.h>using namespace std;#define LL __int64#define maxn 703000#define eps 1e-13#define zero(x) (fabs(x)<eps?0:x)double dp[maxn];int main(){    int n,m;    while(~scanf("%d%d",&m,&n))    {        dp[0]=1.0;        dp[1]=1.0/m;        int i;        for(i=2;i<=n;i++)        {            dp[i]=dp[i-1]+dp[i-1]*1.0/m;            if(i>m)dp[i]=dp[i]-dp[i-m-1]*1.0/m;            if((zero(dp[i]-dp[i-1])==0))            {                printf("%.5lf\n",dp[i]);                break;            }        }        if(i>n)printf("%.5lf\n",dp[n]);    }    return 0;}

Bestcoder round # 7-A, B, c