90 lines
2.2 KiB
C++
90 lines
2.2 KiB
C++
#include <iostream>
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#include <cstdio>
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#include <cstring>
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#include <ctime>
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#include <cstdlib>
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#include <algorithm>
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#include <cmath>
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#include <queue>
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#include <stack>
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#include <vector>
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using namespace std;
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const int maxn=1e5+10;
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const double eps=1e-8;
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const int INF=2e9;
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struct node{
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int id,num0,num1;
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double rate;
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}e[maxn],f,g;
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int t,a[maxn];
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stack<node>mm;
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int main()
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{
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int T;
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scanf("%d",&T);
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while(T--)
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{
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int i,j,k,n,p,q;
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double num,ans=0;
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t=0;
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scanf("%d",&n);
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int l=0,r=n-1;
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for(i=0;i<n;i++)scanf("%d",&a[i]);
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a[n]=1;
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while(a[l]==0)l++;
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while(a[r]==1)r--;
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if(l>r){printf("0.000000\n");continue;}
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for(i=l;i<=r;)
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{
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j=k=0;
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while(a[i]==1){i++;j++;}
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while(a[i]==0){i++;k++;}
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e[t].id=t;e[t].num1=j;e[t].num0=k;e[t].rate=1.0*j/(j+k);
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t++;
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}
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while(!mm.empty())mm.pop();
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for(i=0;i<t;i++)
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{
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if(mm.empty())mm.push(e[i]);
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else
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{
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f=mm.top();
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if(f.rate<=e[i].rate)mm.push(e[i]);
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else
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{
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g=e[i];
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while(true)
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{
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f=mm.top();
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if(f.rate>g.rate)
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{
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g.num1+=f.num1;
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g.num0+=f.num0;
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g.rate=1.0*g.num1/(g.num0+g.num1);
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mm.pop();
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}
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else
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{
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mm.push(g);
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break;
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}
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if(mm.empty())
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{
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mm.push(g);
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break;
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}
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}
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}
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}
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}
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while(!mm.empty())
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{
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f=mm.top();
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mm.pop();
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ans+=f.rate*f.rate*f.num0+(1-f.rate)*(1-f.rate)*f.num1;
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}
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printf("%.6f\n",ans);
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}
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return 0;
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}
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