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

   
   
   
   

    
    
    
    2
abcabcabca
4
abcabcabcabc
3
   
   
   
   

 

Sample Output

   
   
   
   

    
    
    
    0
55
   
   
   
   

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。