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  • hdu5672 尺取法

    StringTime Limit: 2000/1000 MS (Java/Others)    Memory Limit: 65536/65536 K (Java/Others)
    Total Submission(s): 1077    Accepted Submission(s): 348


    Problem Description
    There is a string S.S only contain lower case English character.(10length(S)1,000,000)
    How many substrings there are that contain at least k(1k26) distinct characters?
     
    Input
    There are multiple test cases. The first line of input contains an integer T(1T10) indicating the number of test cases. For each test case:

    The first line contains string S.
    The second line contains a integer k(1k26).
     
    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
    题目大意:给你一个由小写字母组成的字符串,然后给你一个k,表示至少有k个不同的字母,问满足该条件的
    所有的字串的数目。
    思路分析:尺取法基本思路是:
                1.初始化左右端点

        2.不断扩大右端点,直到满足条件

        3.如果第二步中无法满足条件,则终止,否则更新结果

        4.将左端点扩大1,然后回到第二步

    在本题就是先不断扩大右端点,直到满足cut>=k,然后开始移动左端点,并累加子串数目,弱不满足,则继续

    右移右端点,直到下一次满足条件。

    代码:#include <iostream>
    #include <cstdio>
    #include <cstring>
    #include <algorithm>
    #include <map>
    #include <string>
    using namespace std;
    const int maxn=30;
    int q[maxn];
    int main()
    {
        int T;
        string s;
        int k;
        scanf("%d",&T);
        while(T--)
        {
            cin>>s;
            scanf("%d",&k);
            int l=s.length();
            int t=0,cut=0;
            long long  sum=0;
            memset(q,0,sizeof(q));
            for(int i=0;i<l;i++)
            {
                int p=s[i]-'a';
                if(q[p]==0)
                    cut++;
                q[p]++;
                while(cut>=k)
                {
                    sum+=l-i;
                    q[s[t]-'a']--;
                    if(q[s[t]-'a']==0)
                        cut--;
                    t++;//t代表子串开始位置
                }
            }
         cout<<sum<<endl;
        }
        return 0;
    }

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  • 原文地址:https://www.cnblogs.com/xuejianye/p/5441447.html
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