LeetCode OJ Implement strStr()

Implement strStr().

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

http://blog.jobbole.com/52830/

http://www.stoimen.com/blog/2012/04/17/computer-algorithms-boyer-moore-string-search-and-matching/

http://www.ruanyifeng.com/blog/2013/05/boyer-moore_string_search_algorithm.html

class Solution {public:    char *strStr(char *haystack, char *needle) {        int i = BoyerMoore(needle, haystack);        if (i == -1) return NULL;        else return haystack + i;    }    void suffixes(char * pattern, vector<int> & suffixes) {        suffixes[lengthOfPattern - 1] = lengthOfPattern;        int g = lengthOfPattern - 1;        int f;        for (int i = lengthOfPattern - 2; i >= 0; i--) {            if (i > g && suffixes[i + lengthOfPattern - 1 - f] < i - g) {                suffixes[i] = suffixes[i + lengthOfPattern - 1 - f];            } else {                if (i < g) {                    g = i;                }                f = i;                while (g >= 0 && pattern[g] == pattern[g + lengthOfPattern - 1 - f]) {                    g--;                }                suffixes[i] = f - g;            }        }    }    void findBadCharacters(char * pattern, vector<int> & badCharacters) {        for (int i = 0; i < lengthOfPattern - 1; i++) {            badCharacters[pattern[i]] = lengthOfPattern - i - 1;        }    }    void findGoodSuffixes(char * pattern, vector<int> & goodSuffixes) {        vector<int> suff(lengthOfPattern, 0);        suffixes(pattern, suff);                for (int i = 0; i < lengthOfPattern; i++) {            goodSuffixes[i] = lengthOfPattern;        }        int j = 0;        for (int i = lengthOfPattern - 1; i >= 0; i--) {            if (suff[i] == i + 1) {                for (; j < lengthOfPattern - i - 1; j++) {                    if (goodSuffixes[j] == lengthOfPattern) {                        goodSuffixes[j] = lengthOfPattern - i - 1;                    }                }            }        }        for (int i = 0; i <= lengthOfPattern - 2; i++) {            goodSuffixes[lengthOfPattern - 1 - suff[i]] = lengthOfPattern - i - 1;        }    }    int BoyerMoore(char * pattern, char * text) {        lengthOfText = strlen(text);        lengthOfPattern = strlen(pattern);        // some specil cases        if (lengthOfPattern == 0 && lengthOfText == 0) return 0;        if (lengthOfPattern == lengthOfText) {            for (int i = 0; i < lengthOfText; i++) {                if (pattern[i] != text[i]) return -1;            }            return 0;        }        if (lengthOfPattern == 0) return lengthOfText - 1;        if (lengthOfText == 0) return -1;                goodSuffixes.resize(lengthOfPattern);        badCharacters.resize(256);        findGoodSuffixes(pattern, goodSuffixes);        findBadCharacters(pattern, badCharacters);        int j = 0;        while (j <= lengthOfText - lengthOfPattern) {            int i;            for (i = lengthOfPattern - 1; i >= 0 && pattern[i] == text[i + j]; i--);            if (i < 0) {                return j;  // return the first matching position                //cout << j << endl;  // output every position that is the head of a matching                j += goodSuffixes[0];            } else {                j += max(goodSuffixes[i], badCharacters[text[i + j]] - lengthOfPattern + i + 1);            }        }        return -1;    }private:    vector<int> goodSuffixes;    vector<int> badCharacters;    int lengthOfPattern;    int lengthOfText;};