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
使用KMP算法来overwrite strStr()
class Solution { public: int strStr(string haystack, string needle) { if(needle.empty()) return 0; if(haystack.empty()) return -1; return kmp(haystack, needle); } int kmp(string haystack, string needle) { vector<int> next = getNext(needle); int sLen = haystack.size(), tLen = needle.size(); int i = 0, j = 0, res = -1; while (i < sLen) { if (j == -1 || haystack[i] == needle[j]) { ++i; ++j; } else { j = next[j]; } if (j == tLen) { res = i - tLen; break; } } return res; } vector<int> getNext(string needle) { vector<int> next(needle.size(), -1); int tLen = needle.size(); int i = 0, j = -1; while (i < tLen - 1) { if (j == -1 || needle[i] == needle[j]) { ++i; ++j; next[i] = j; } else { j = next[j]; } } return next; } }; // 7 ms
