C + + KMP algorithm

KMP algorithm is an improved string matching algorithm, which is found by D.e.knuth and V.r.pratt and J.h.morris, so it is called the Knut-Morris-Pratt operation (the KMP algorithm).

The key of the KMP algorithm is to define a next function according to the given pattern string w1,m, and the next function contains the local matching information of the pattern string itself.

#include <iostream> #include <cstring> #include <string> #include <set> #include <map>    Using namespace std;void buildpatchmatchtable (int *partmatchtable, char *findstr) {if (findstr = = NULL) return;    Partmatchtable[0] = 0;    int sizefind = strlen (findstr);        for (int i = 1; i < Sizefind; ++i) {set<string> preset;        String tmppre = "";        Tmppre = findstr[0];        Preset.insert (Tmppre);            for (int j = 1; j < i; ++j) {tmppre = Tmppre + findstr[j];        Preset.insert (Tmppre);        } set<string> Postset;        String tmppost = "";        Tmppost = Findstr[i];        Postset.insert (Tmppost);            for (int j = i-1; j > 0;--j) {tmppost = findstr[j] + tmppost;        Postset.insert (Tmppost);        } set<string> Comset; for (Set<string>::iterator beg = Preset.begin (); Beg! = Preset.end (); ++beg) {if (PostseT.count (*beg) > 0) comset.insert (*beg);        } int maxlen = 0; for (Set<string>::iterator beg = Comset.begin (); Beg! = Comset.end (); ++beg) {if ((*beg). Size () ;        MaxLen) MaxLen = (*beg). Size ();    } Partmatchtable[i] = MaxLen;    }}int KMP (Char *srcstr, char *findstr) {if (Srcstr = = NULL | | findstr = null) return-1;    int lensrc = strlen (SRCSTR);    int lenfind = strlen (findstr);    int *partmatchtable = new Int[lenfind];    Buildpatchmatchtable (partmatchtable, findstr); for (int i = 0; i < lenfind; ++i) cout << findstr[i] << "\ t" << Partmatchtable[i] << Endl    ;    int curfind = 0;    for (int i = 0; i < lensrc;)            {if (findstr[curfind] = = Srcstr[i]) {++i;        ++curfind;            } else {if (Curfind = = 0) ++i; else {int movestep = Curfind-partmATCHTABLE[CURFIND-1];                i + = Movestep;            Curfind = 0;            }} if (Curfind = = lenfind) {delete []partmatchtable;        return i-lenfind;    }} return-1; delete []partmatchtable;}    int main () {char srcstr[] = "Bbcabcdababcdabcdabde";    Char findstr[] = "ABCDABD";    cout << "POS:" << kmp (Srcstr, findStr) << Endl;    Char srcstr2[] = "substring searching algorithm search";    Char findstr2[] = "search"; cout << "POS:" << kmp (SRCSTR2, findStr2) << Endl;}

C + + KMP algorithm