28. Implement strStr()
Implement strStr().
Returns the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.
字符串Rabin--Karp算法。滚动哈希,时间复杂度o(n+m),觉得比kmp好写
class Solution { public: const unsigned long long T = 100000007; int strStr(string haystack, string needle) { typedef unsigned long long ull; int al = needle.length(); int bl = haystack.length(); if (al > bl) return -1; ull A = 0; ull B = 0; ull t = 1; for (int i = 0; i < al; ++i) { A = A * T + needle[i]; B = B * T + haystack[i]; t *= T; } //cout << A << " "<<B<<endl; for (int i = 0; i + al <= bl; ++i) { if (A == B) return i; if (i + al < bl) B = B * T - t * haystack[i] + haystack[i + al]; } return -1; } };
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