cf B Bear and Strings

题意：给你一个字符串，然后找多少区间内含有“bear”，输出数目；

 1 #include <cstdio>

 2 #include <cstring>

 3 #include <algorithm>

 4 using namespace std;

 5 

 6 char str[5001];

 7 int pos[50001];

 8 

 9 int main()

10 {

11     while(scanf("%s",str)!=EOF)

12     {

13         int k=strlen(str);

14         memset(pos,0,sizeof(pos));

15         int cnt=0;

16         for(int i=0; i+4<=k; i++)

17         {

18             if(str[i]=='b'&&str[i+1]=='e'&&str[i+2]=='a'&&str[i+3]=='r')

19             {

20                 pos[cnt++]=i+3;

21             }

22         }

23         int ans=0;

24         int last=0;

25         for(int i=0; i<cnt; i++)

26         {

27             if(pos[i]-3==0)

28             {

29             ans+=(k-pos[i]);

30 

31             last=pos[i]-3;

32             }

33             else

34             {

35                 if(i==0)

36                 {

37                     ans+=(pos[i]-3+1)*(k-pos[i]);

38                 }

39                 else

40                 ans+=(pos[i]-3-last)*(k-pos[i]);

41                 last=pos[i]-3;

42             }

43         }

44         printf("%d\n",ans);

45     }

46     return 0;

47 }

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