hdu 5672 String

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 65536/65536 K (Java/Others)
Total Submission(s): 2370    Accepted Submission(s): 780

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

 

Source

BestCoder Round #81 (div.2)

 

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求包含不同字母数不小于k的子串数。尺取法，两个下标移动，当tail移动到head~tail包含了k个不同的字母时，ans就加len - tail + 1,加上后面的字母组成的子串满足条件，然后移动head，每次移动ans都加len - tail + 1,直到head~tail包含不同的字母不足k时再次移动tail。

 

代码：

#include <iostream>
#include <cstdio>
#include <cstring>
#define inf 0x3f3f3f3f
#define MAX 302
using namespace std;
int main() {
    int t,k,v[30];
    char s[1000005];
    scanf("%d",&t);
    while(t --) {
        scanf("%s%d",s,&k);
        long long ans = 0;
        int len = strlen(s);
        int c = 0;
        memset(v,0,sizeof(v));
        int head = 0,tail = 0;
        while(tail < len) {
            int d = s[tail ++] - 'a';
            if(!v[d]) c ++;
            v[d] ++;
            if(c >= k) {
                while(head <= tail) {
                    int e = s[head ++] - 'a';
                    v[e] --;
                    ans += len - tail + 1;
                    if(!v[e]) {
                        c --;
                        break;
                    }
                }
            }
        }
        printf("%lld
",ans);
    }
}