Implement strStr()--字符串匹配_kmp_bkdHash

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Implement strStr().

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

两种方法：

1）bkdHash

2）kmp

代码分别如下：

//bkdHash

int strStr(string haystack, string needle) {        typedef unsigned long long ull;         int size1 = haystack.size(), size2 = needle.size();        if(size1<size2) return -1;        ull* Hash = new ull[size1+1];        ull nbase = 1; //因为size2是知道的，不用计算nbase[i]        int i, base = 31;        //并给haystack建立bkdHash        Hash[0] = 0;        for(i = 1; i <= size1; ++i)            Hash[i] = Hash[i-1]*base + haystack[i-1] - 'a' + 1;        //计算needle的hash值, 计算nbase,        ull h = 0;        for(i = 0; i < size2; ++i){            nbase = nbase*base;            h = h*base + needle[i] - 'a' + 1;        }        for(i = size2; i <= size1; ++i)            if(Hash[i] - Hash[i-size2]*nbase==h) return i-size2;        delete [] Hash;        return -1;    }

    //kmp    int strStr(string haystack, string needle) {        int size1 = haystack.size(), size2 = needle.size();        if(size1<size2) return -1;        if(needle=="") return 0;        int *next = getNext(needle);        int i, j = 0;        for(i = 0; i < size1; ++i){            if(j==-1||haystack[i]==needle[j]){                if(++j==size2) return i-j+1;            }            else{                j = next[j];                i--;            }        }        delete [] next;        return -1;    }    //next数组    int* getNext(string& needle){        int i, j, size = needle.size();        int *next = new int[size];        memset(next, 0, sizeof(int)*size);        next[0] = -1;        for(i = 1; i < size; ++i){            j = i-1;            while(next[j]>=0){                if(needle[i-1]==needle[next[j]]){                    next[i] = next[j] + 1;                    break;                }                else j = next[j];            }        }        return next;    }

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