KMP模式匹配

#include<iostream>#include<stdio.h>#include<string>#include<algorithm>using namespace std;int find_kmp(string p,string s,int* next){int i=0,j=0;//从第一个字符开始，i为模式的索引，j为原串的索引int m=p.size(),n=s.size();//长度while(i<m&&j<n)if(p[i]==s[j]){++i;++j;}else //p[i]!=s[j]{if(next[i]!=-1)i=next[i];else{i=0;++j;}}if(i>=m)return j-i+1;else return -1;}void comp_next(string p,int next[]){int k=-1,i=0,m=p.size();next[0]=-1;while(i<m-1){while(k!=-1&&p[k]!=p[i])k=next[k];++i;++k;if(p[i]==p[k])next[i]=next[k];elsenext[i]=k;}} /*这种的写法结构比较好理解，而上面书写上做了 一定得修改，但不易理解*//*void comp_next(string p,int next[]){int k=-1,i=0,m=p.size();next[0]=-1;while(i<m-1){if(k==-1||p[i]==p[k]){++k;++i;if(p[i]==p[k])next[i]=next[k];elsenext[i]=k;}elsek=next[k];}}*/int main(){const int maxsize=20;string s="acabaabaabcacaabc";string p="abaabcac";int next[maxsize];cout<<"源串s="<<s<<endl;cout<<"模式串p="<<p<<endl;cout<<"p的首次出现位置："<<s.find(p)<<endl;//comp_next(p,next);int len=p.size();for(int i=0;i<len;i++)cout<<next[i]<<" ";cout<<endl;cout<<"/np的首次出现位置："<<find_kmp(p,s,next)<<endl;return 0;}/*//原始的匹配方法int find(string p,string s)//p为模式串{int i=0,j=0;//从第一个字符开始，i为模式的索引，j为源串的索引int m=p.size(),n=s.size();//取长度while(i<m&&j<n)if(p[i]==s[j]){++i;++j;}else{j=j-i+1;i=0;}if(i==m)return j-i+1;//找到else return -1; //没找到}*/

// string::find#include <iostream>#include <string>using namespace std;int main (){ string str ("There are two needles in this haystack with needles."); string str2 ("needle"); size_t found; found=str.find(str2); if (found!=string::npos) cout << "first 'needle' found at: " << int(found) << endl;}//ouput://first 'needle' found at: 14