KMP排序

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我是靠谱客的博主无奈斑马，最近开发中收集的这篇文章主要介绍KMP排序，觉得挺不错的，现在分享给大家，希望可以做个参考。

概述

Implement strStr().

Return the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.

Example 1:

Input: haystack = "hello", needle = "ll"
Output: 2

Example 2:

Input: haystack = "aaaaa", needle = "bba"
Output: -1

class Solution {
public:
    
      //普通字符串匹配    
      int strStr(string haystack, string needle) {
        if(haystack.empty()&&needle.empty())
            return 0;
        int n = haystack.length();
        int m = needle.length();
        int i;
        for(i=0; i<n; i++)
        {
            int j;
            for(j=0; j<m; j++)
            {
                if(needle[j]!=haystack[i+j])
                    break;
            }
            if(j==m)
                break;
        }
        return i==n ? -1 : i;
        
    }
    
    //KMP算法
    void MakeNext(string pattern, int *next)
    {
        int k=0;
        int m = pattern.length();
        next[0] = 0;
        int i=0;
        for(i=1; i<m; i++)
        {
            while(k>0&&pattern[i]!=pattern[k])
                k = next[k-1];
            if(pattern[i] == pattern[k])
                k++;
            next[i] = k;
          
        }
    }
    
    int strStr(string haystack, string needle) {
        if((haystack.empty()|| !haystack.empty())&&needle.empty())
            return 0;
        int n = haystack.length();
        int m = needle.length();
        int *next = new int[m];
        MakeNext(needle, next);
        int i,p;
        cout<<n<<"@"<<m<<endl;
        for(i=0,p=0;i<n; i++)
        {
         
            while(p>0&&haystack[i]!=needle[p])
                p = next[p-1];
            if(haystack[i]==needle[p])
                p++;
            if(p==m)
            {
                cout<<"pattern"<<endl;
                return i-m+1;
            }
        }
        cout<<i<<" "<<p<<endl;
        return -1;
    }

    
};