面试题30：KMP 字符串查找

参考：http://www.ruanyifeng.com/blog/2013/05/Knuth%E2%80%93Morris%E2%80%93Pratt_algorithm.html
自己写的很简单的KMP字符串匹配

int KMP(string s,string p){
    int pLen = p.length();
    int* next = new int[pLen];
    next[0] = -1;

    int k = -1;
    int j = 0;
    while(j < pLen - 1){
        if(k == -1 || p[k] == p[j]){
            k++;
            j++;
            next[j] = k;
        }else{
            k = next[k];
        }
    }

    //print next array;
    for(int k=0;k<pLen;k++){
        std::cout << next[k]<< ",";
    }
    std::cout << std::endl;

    j = 0;
    size_t i = 0;
    size_t sLen = s.length();
    while(i<sLen && j < pLen){
        if(j == -1 || s[i] == p[j]){
            i++;
            j++;
        }else{
            j = next[j];
        }
    }

    delete next;
    if(j == pLen){
        return i - j;
    }else{
        return -1;
    }
}

Implement strStr().

Returns a pointer to the first occurrence of needle in haystack, or null if needle is not part of haystack.

class Solution {
public:
    char *strStr(char *haystack, char *needle) {
        if(haystack == nullptr || needle == nullptr) return nullptr;

        int i = 0,j =0;
        int start = 0;
        while(haystack[i] != '' && needle[j] != ''){
            if(haystack[i] == needle[j]){
                i++;
                j++;
            }else{
                start++;
                i = start;
                j = 0;
            }
        }
        if(needle[j] == '') return haystack+start;
        else return nullptr;
    }
};