模式字符串匹配问题（KMP算法）

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

/**

字符串模式匹配的朴素算法

s为偏移量

*/

#include <cstdio>

#include <iostream>

#include <cstring>

using
namespace std;

const
int maxlen = 1000;

void
NAIVE_STRING_MATCHER(char* stra, char* strb)

{

    int
n(strlen(stra)), m(strlen(strb));

    for
(int s(0);s <= n - m; ++s)

        if
(stra[s] == strb[0])

        {

            bool
flag = true;

            for
(int i(0); i < m; ++i)

                if
(stra[s+i] != strb[i])

                {

                    flag = false;

                    break;

                }

            if
(flag)

            {

                cout<<"Pattern occurs with shifts "<<s<<endl;

                return;

            }

        }

    cout<<"Pattern doesn‘t occur."<<endl;

}

int
main()

{

    char
stra[maxlen], strb[maxlen];

    while(cin>>stra && cin>>strb)

        NAIVE_STRING_MATCHER(stra, strb);

    return
0;

}

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

41

42

43

44

45

46

47

48

49

/**

Rabin, Karp 发现的字符串匹配算法

*/

#include <cstdio>

#include <iostream>

#include <cstring>

using
namespace std;

const
int maxlen = 10000;

int d(10), mod(100000007);

void
RABIN_KARP_MATCHER(char* stra, char* strb)

{

    int
n(strlen(stra)), m(strlen(strb)), p(0), t(0), h(1);

    //preprocessing

    for
(int i(0); i < m-1; ++i)

        h = i ? h * d % mod : d % mod;

    for
(int i(0); i < m; ++i)

    {

        p = (d * p + strb[i]) % mod;

        t = (d * t + stra[i]) % mod;

    }

    for
(int s(0); s <= n - m; ++s)

    {

        if
(p == t)

        {

            bool
flag = true;

            for
(int j(0); j < m; ++j)

                if
(stra[s+j] != strb[j])

                {

                    flag = false;

                    break;

                }

            if
(flag)

            {

                cout<<"Pattern occurs with shifts "<<s<<endl;

                return
;

            }

        }

        t = (d * (t - (stra[s]) * h) + stra[s+m]) % mod;

    }

    cout<<"Pattern doesn‘t occur."<<endl;

}

int
main()

{

    char
stra[maxlen], strb[maxlen];

    while(cin>>stra && cin>>strb)

        RABIN_KARP_MATCHER(stra, strb);

    return
0;

}

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

41

42

43

44

45

46

47

48

49

#include <cstdio>

#include <iostream>

#include <algorithm>

#include <cstring>

using
namespace std;

const
int maxlen = 10000;

void
get_next(char* strb, int* next)

{

    int
i(1), j(-1), d(strlen(strb));

    next[0] = -1;

    for
(; i < d; ++i)

    {

        while(j >= 0 && strb[j+1] != strb[i])

            j = next[j];

        if
(strb[j+1] == strb[i])

            j += 1;

        next[i] = j;

    }

}

void
KMP_MATCHER(char* stra, char* strb)

{

    int
n(strlen(stra)), m(strlen(strb)), next[maxlen];

    get_next(strb, next);

    int
i(0), j(-1);

    for
(int i(0); i < n; ++i)

    {

        while(j >= 0 && strb[j+1] != stra[i])

            j = next[j];

        if
(strb[j+1] == stra[i])

            j += 1;

        if
(j == m - 1)

        {

            cout<<"Pattern occurs with shifts "<<i - j<<endl;

            return
;

        }

    }

    cout<<"Pattern doesn‘t occurs."<<endl;

}

int
main()

{

    char
stra[maxlen], strb[maxlen];

    while(cin>>stra && cin>>strb)

        KMP_MATCHER(stra, strb);

    return
0;

}