28. Implement strStr()

Problem's Link

----------------------------------------------------------------------------

Mean:

给定两个字符串str1和str2，输出str2在str1中第一次出现的下标.

analyse:

KMP算法模板题.

Time complexity: O(N)

view code

/**
* -----------------------------------------------------------------
* Copyright (c) 2016 crazyacking.All rights reserved.
* -----------------------------------------------------------------
* Author: crazyacking
* Date : 2016-02-19-16.45
*/
#include <queue>
#include <cstdio>
#include <set>
#include <string>
#include <stack>
#include <cmath>
#include <climits>
#include <map>
#include <cstdlib>
#include <iostream>
#include <vector>
#include <algorithm>
#include <cstring>
using namespace std;
typedef long long(LL);
typedef unsigned long long(ULL);
const double eps(1e-8);

class Solution
{
public:
int Next[100005];
void getNext(string& s)
{
Next[0]=0;
for(int i=1,k=0;i<s.length();++i)
{
while(s[i]!=s[k] && k)
k=Next[k-1];
if(s[i]==s[k])
++k;
Next[i]=k;
}
}
int strStr(string haystack, string needle)
{
if(needle.length()==0)
return 0;
getNext(needle);
for(int i=0,k=0;i<haystack.length();++i)
{
while(haystack[i]!=needle[k] && k)
k=Next[k-1];
if(haystack[i]==needle[k])
++k;
if(k==needle.length())
return i-k+1;
}
return -1;
}
};

int main()
{
string str1,str2;
while(cin>>str1>>str2)
{
Solution solution;
cout<<solution.strStr(str1,str2)<<endl;
}
return 0;
}
/*

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LeetCode - 28. Implement strStr()

28. Implement strStr()

Problem's Link

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