CF 108b Basketball team combinatorial Math

Test instructions

A university has m college, each college has SI individuals, now to form a team of n people, already know the hero in the first H college, and he was first accepted by the team, now the college in the remainder of the average probability of the selection of n-1 personal

Q: The hero wants to know if there are people in the team and he is from the same college, if not enough, then output-1

This is a simple combinatorial math problem, but be aware that the intermediate process of calculation overflows.

1#include <cstdio>2 3 Const intmaxn=1010;4 #defineLL Long Long5 6 intS[MAXN];7 8 intMain ()9 {Ten     intn,m,h; Onescanf"%d%d%d",&n,&m,&h); A     intsum=0; -      for(intI=1; i<=m;i++) -     { thescanf"%d",&s[i]); -sum+=S[i]; -     } -     if(sum<N) +     { -printf"-1\n"); +     } A     Else if(s[h]==1) at     { -printf"0\n"); -     } -     Else if(sum-s[h]<n-1) -     { -printf"1\n"); in     } -     Else to     { +s[h]--; -sum--; the         DoubleCnta=1; *          for(LL i=sum-s[h]-n+2; i<=sum-n+1; i++) $         {Panax Notoginsengcnta*=i; -         } the          for(LL i=sum-s[h]+1; i<=sum;i++) +         { Acnta=cnta/i; the         } +printf"%.6f\n",1.0-(Double) cnta); -     } $  $     return 0; -}

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CF 108b Basketball team combinatorial Math