string 匹配

题目描述

 Finding all occurrences of a pattern in a text is a problem that arises frequently in text-editing programs.     Typically,the text is a document being edited,and the pattern searched for is a particular word supplied by the user.       We assume that the text is an array T[1..n] of length n and that the pattern is an array P[1..m] of length m<=n.We further assume that the elements of P and  T are all alphabets(∑={a,b...,z}).The character arrays P and T are often called strings of characters.       We say that pattern P occurs with shift s in the text T if 0<=s<=n and T[s+1..s+m] = P[1..m](that is if T[s+j]=P[j],for 1<=j<=m).       If P occurs with shift s in T,then we call s a valid shift;otherwise,we calls a invalid shift.      Your task is to calculate the number of vald shifts for the given text T and p attern P.

输入描述:

For each case, there are two strings T and P on a line,separated by a single space.You may assume both the length of T and P will not exceed 10^6.

输出描述:

You should output a number on a separate line,which indicates the number of valid shifts for the given text T and pattern P.

示例1

abababab abab

3

代码

#include<iostream>
#include<string>
using namespace std;

int main()
{
    string s1;
    string s2;
    while(cin>>s1>>s2)
    {
        int length1 = s1.length();
        int length2 = s2.length();
        if(length2>length1)
            cout<<0;
        else{
            int num=0;
            while(s1.length()>=length2)
            {
                int pos=s1.find(s2);
                if(pos>=0)
                {
                    s1 = s1.substr(pos+1);
                    num++;
                }

            }
            cout<<num<<endl;
        }
    }
}