String HDU5672

Problem Description

There is a string S.S only contain lower case English character.(10≤length(S)≤1,000,000)
How many substrings there are that contain at least k(1≤k≤26) distinct characters?

 

Input

There are multiple test cases. The first line of input contains an integer T(1≤T≤10) indicating the number of test cases. For each test case:

The first line contains string S.
The second line contains a integer k(1≤k≤26).

 

Output

For each test case, output the number of substrings that contain at least k dictinct characters.

 

Sample Input

2abcabcabca4abcabcabcabc3

 

Sample Output

055

大意：

在一个字符串中任意取子串，求其至少有K个不同字母的子串个数。

#include<iostream>#include<cstring>#include<stdio.h>using namespace std;char str[1001000];int num[26],k;int main(){    //freopen("in.txt","r",stdin);    int T;    cin>>T;    while(T--)    {        long long ans=0;        memset(num,0,sizeof(num));        cin>>(str+1)>>k;        int cur=0,r=0,l=1,len=strlen(str+1);        while(l<=len)        {        while(r<len&&cur<k)        {            r++;            if(num[str[r]-'a']==0)                cur++;            num[str[r]-'a']++;        }        if(cur==k)        {             ans+=len-r+1;             num[str[l]-'a']--;             if(num[str[l++]-'a']==0)                cur--;             while(num[str[l-1]-'a'])             {                 ans+=len-r+1;                 num[str[l]-'a']--;                if(num[str[l++]-'a']==0)                  cur--;             }        }        else            break;        }        cout<<ans<<endl;    }}

大体思路就是两个指针（数组下标）从左到右指，每次都使指中的区域不同字母数为K，加上所有情况。

切记，代码越简明越好。