CodeForces-1238D-AB-string CodeForces-思维+字符串反向思考

The string $t_{1} t_{2} \dots t_{k}$

A palindrome is a string that reads the same backward as forward. For example, the strings A, BAB, ABBA, BAABBBAAB are palindromes, but the strings AB, ABBBAA, BBBA are not.

Here are some examples of good strings:

You are given a string $s$

You have to calculate the number of good substrings of string $s$

Input

The first line contains one integer $n$

The second line contains the string $s$

Output

Print one integer — the number of good substrings of string $s$

Examples

Input

5
AABBB

Output

Input

3
AAA

Output

Input

7
AAABABB

Output

Note

In the first test case there are six good substrings: $s_{1} \dots s_{2}$

In the second test case there are three good substrings: $s_{1} \dots s_{2}$

 1 #include<stdio.h>
 2 #include<string.h>
 3 const int N=300020;
 4 typedef long long ll;
 5 
 6 char a[N],b[N];
 7 
 8 int main()
 9 {
10     ll n;
11     while(~scanf("%lld",&n))
12     {
13         scanf("%s",a);
14         ll sum1=0,sum2=0,ss=0;
15         int k1=0,k2=0;
16         for(int i=1;i<n;i++)
17         {
18             if(a[i]!=a[i-1])
19             {
20                 ss++;
21                 sum1=sum1+i-k1;
22                 k1=i;
23             }
24         }
25 
26         int p=0;
27         for(int i=n-1;i>=0;i--)
28             b[p++]=a[i];
29         for(int i=0;i<p;i++)
30         {
31             if(b[i]!=b[i-1])
32             {
33                 sum2=sum2+i-k2;
34                 k2=i;
35             }
36         }
37         ll w=n*(n-1)/2-sum1-sum2+ss;
38         printf("%lld\n",w);
39     }
40     return 0;                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
41 }