[2016-04-14] [Codeforces] [630] C [Lucky Numbers]

• Time: 2016-04-14-23:12:27 Thursday
• Title Number: [2016-04-14][codeforces][630][c][Lucky Numbers]
• Main topic:
  • Ask how many lucky numbers are within n digits
  • Lucky numbers: Numbers that contain only 7,8
• Analysis:
  • The lucky number of the length I, each one has two possibilities, 7, 8, then the lucky number of length I has a total of $2^i$ may
  • Then all the lucky numbers within the length of n are $2^1 + 2^2 + ... + 2^n$,

  
 

   
  

  
#include<cstdio>
   
  

  
using namespace std;
   
  

  
typedef long long ll;
   
  

  
int main(){
   
  

  
 int n;ll ans = 0,cur = 1;
   
  

  
 scanf("%d",&n);
   
  

  
 while(n--){
   
  

  
 cur *= 2;
   
  

  
 ans += cur;
   
  

  
 }
   
  

  
 printf("%I64d\n",ans);
   
  

  
}
  
 

From for notes (Wiz)

[2016-04-14] [Codeforces] [630] C [Lucky Numbers]