Round #411 (Div.2)

A. Fake NP
time limit per test
1 second
memory limit per test
256 megabytes
input
standard input
output
standard output

Tavak and Seyyed are good friends. Seyyed is very funny and he told Tavak to solve the following problem instead of longest-path.

You are given l and r. For all integers from l to r, inclusive, we wrote down all of their integer divisors except 1. Find the integer that we wrote down the maximum number of times.

Solve the problem to show that it's not a NP problem.

 
Input

The first line contains two integers l and r (2 ≤ l ≤ r ≤ 109).

 
Output

Print single integer, the integer that appears maximum number of times in the divisors.

If there are multiple answers, print any of them.

 
Examples
 
Input
19 29
 
Output
2
 
Input
3 6
 
Output
3
 
Note

Definition of a divisor: https://www.mathsisfun.com/definitions/divisor-of-an-integer-.html

The first example: from 19 to 29 these numbers are divisible by 2: {20, 22, 24, 26, 28}.

The second example: from 3 to 6 these numbers are divisible by 3: {3, 6}.

题意：求因子

1 #include <bits/stdc++.h>
2 using namespace std;
3 int main(){  
4     int l,r;
5     scanf("%d%d",&l,&r);
6     if(l==r) printf("%d\n",l);
7     else printf("2\n");      
8 
9 }

 

 

D. Minimum number of steps
time limit per test
1 second
memory limit per test
256 megabytes
input
standard input
output
standard output

We have a string of letters 'a' and 'b'. We want to perform some operations on it. On each step we choose one of substrings "ab" in the string and replace it with the string "bba". If we have no "ab" as a substring, our job is done. Print the minimum number of steps we should perform to make our job done modulo 109 + 7.

The string "ab" appears as a substring if there is a letter 'b' right after the letter 'a' somewhere in the string.

 
Input

The first line contains the initial string consisting of letters 'a' and 'b' only with length from 1 to 106.

 
Output

Print the minimum number of steps modulo 109 + 7.

 
Examples
Input
ab
 
Output
1
 
Input
aab
Output
3
 
Note

The first example: "ab"  →  "bba".

The second example: "aab"  →  "abba"  →  "bbaba"  →  "bbbbaa".

 

 1 #include <bits/stdc++.h>
 2 using namespace std;
 3 const int mod=1e9+7;
 4 int main(){
 5     string s;
 6     cin>>s;
 7     int ans=0;
 8     int t=0;
 9     for(int i=s.length()-1;i>=0;i--){
10         if(s[i]=='b')
11             t=(t+1)%mod;
12         else {
13         ans=(ans+t)%mod;
14         t=(t*2)%mod;
15         }
16     }
17     cout<<ans<<endl;
18     return 0;
19 }

 

 

posted @ 2017-09-20 15:22  浅忆~  阅读(152)  评论(0)  编辑  收藏  举报