【leetcode c++】28 Implement strStr()
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Implement strStr().
Returns the index of the first occurrenceof needle in haystack, or -1 if needle is not part of haystack.
实现子字符串查找功能。
犹记得清华大学出版社的数据结构书上,那神奇的KMP算法……
KMP请自行百度。
这里我用了BM算法(只用到了delta1),BM算法也请自行百度。这两个算法的图解太难用电脑绘制。
我也怕自己讲不好。Σ(・ω・;|||
我用的参考书是国外计算机经典教材的C++数据结构与算法。
直接贴源码了。
一开始随便来了个暴力解法,直接超时了。。。顺便,这道题你可以直接这样来测试string.find()的速度:
Leetcode的AcceptedSolutions Runtime Distribution(15-06-08)
源码:(VS2013)
#include <iostream>#include <map>#include <array>using namespace std;int strStr(string haystack, string needle);int main(){cout << strStr("mississippi", "pi");return 0;}int strStr(string haystack, string needle){////////////////////////////////////////////////////////////BM算法(only delta1)if (0 == haystack.size() && 0 == needle.size()) return 0;if (0 == haystack.size()) return -1;if (0 == needle.size()) return 0;int i = 0;int haystackSize = haystack.size();int needleSize = needle.size();int delta[26] = { needleSize, needleSize, needleSize, needleSize, needleSize,needleSize, needleSize, needleSize, needleSize, needleSize,needleSize, needleSize, needleSize, needleSize, needleSize,needleSize, needleSize, needleSize, needleSize, needleSize,needleSize, needleSize, needleSize, needleSize, needleSize,needleSize };for (i = 0; i < needleSize; i++){delta[(int)needle[i] - 97] = needleSize - i - 1;}i = needleSize - 1;int j;while (i < haystackSize){j = needleSize - 1;while (j >= 0 && haystack[i] == needle[j]){i--;j--;}if (-1 == j){return i + 1;}int offset = delta[(int)haystack[i] - 97];i = i + ((offset > (needleSize - j)) ? offset : (needleSize - j));}return -1;}
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