HUD 5056 Boring count

Boring count

You are given a string S consisting of lowercase letters, and your task is counting the number of substring that the number of each lowercase letter in the substring is no more than K.

In the first line there is an integer T , indicates the number of test cases.
For each case, the first line contains a string which only consist of lowercase letters. The second line contains an integer K.

[Technical Specification]
1<=T<= 100
1 <= the length of S <= 100000
1 <= K <= 100000

For each case, output a line contains the answer.

3
abc
1
abcabc
1
abcabc
2

6
15
21

思路：O（n）的算法，枚舉i，求出以每個i結尾的滿足條件的串的個數，即以i結尾的最長串的長度。

源代碼：

#include
#include
#include
#include

#define N 111111
using namespace std;

typedef long long LL;

char str[100001];
int cnt[30];
int k;

int main()
{
    int T;
    cin>>T;
    while(T--)
    {
        cin>>(str+1)>>k;
        memset(cnt,0,sizeof cnt);
        int n=strlen(str+1);
        int pos=0;
        LL res=0;
        for(int i=1;i<=n;i++)
        {
            cnt[str[i]-'a']++;
            if(cnt[str[i]-'a']>k)
            {
                pos++;
                while(str[pos]!=str[i])
                {
                    cnt[str[pos]-'a']--;
                    pos++;
                }
                cnt[str[pos]-'a']--;
            }
            res+=i-pos;
        }
        printf("%I64d\n",res);
    }
    return 0;
}