LeetCode28. Implement strStr () [Simple]-KMP, next []

Title description:

My solution:

I originally forgot about the KMP algorithm. I reviewed it through this question.

Which calculates the next loop while (i <length-1), pay attention to need -1, because there is i ++ below, otherwise it will report an error

It took a long time to find the mistake here

class Solution {
//private:
  //  int next[];
public:
    int* func(string needle){
        int* next=new int[needle.length()];
        int length=needle.length();
        int i=0;
        int j=-1;
        next[0]=-1;
        while(i<length-1){
            if(j==-1 || needle[i]==needle[j]){
                i++;
                j++;
                next[i]=j;
            }
            else    j=next[j];
        }
        return next;
    }
    int strStr(string haystack, string needle) {
        if(needle=="")  return 0;
        if(haystack==""&&needle!="")    return -1;
        if(haystack.length()<needle.length())   return -1;
        int *next=func(needle);
        int i=0,j=0;
        int la=(int)haystack.length(),lb=(int)needle.length();
        while(i<la&&j<lb){
            if(j==-1 || haystack[i]==needle[j]){
                i++;
                j++;
            }
            else    j=next[j];
        }
        return j==lb?i-j:-1;
    }
};