KMP实现

最新推荐文章于 2021-12-19 11:23:05 发布

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本文介绍了一种高效的字符串匹配算法——KMP算法，并通过C++代码详细展示了两种不同的KMP算法实现方式，包括next数组和nextval数组的计算过程。通过对主串和模式串的比较，能够快速定位模式串在主串中的起始位置。

#include<iostream>
#include<string>
#include<stack>
using namespace std;

class Solution{
public:
	void getNext(int* next, const string& s)
	{
		int j = 0;
		next[0] = 0;
		for (int i = 1; i < s.size(); i++)
		{
			while (s[i] != s[j] && j > 0) {
				j = next[j - 1];
			}
			if (s[i] == s[j]) {
				j++;
			}
			next[i] = j;
		}
	}

	//统一减一
	void getnext(int* next, const string& s) {
		int j = -1;
		next[0] = j;
		for (int i = 1; i < s.size(); i++) {
			while (s[i] != s[j+1] && j > -1) {
				j = next[j];
			}
			if (s[i] == s[j+1])
			{
				j++;
			}
			next[i] = j;
		}
	}

	int strStr(string haystack, string needle) {
		if (needle.size() == 0) return 0;
		int size = needle.size();
		int* p =new int[size];
		//int next[needle.size()];
		getNext(p, needle);
		int j = 0;
		for (int i = 0; i < haystack.size(); i++) {
			while (j > 0 && haystack[i] != needle[j]) {
				j = p[j-1];
			}
			if (haystack[i] == needle[j])
			{
				j++;
			}
			if (j == needle.size()) {
				return (i - needle.size() + 1);
			}
		}
		return -1;
	}

	int strStr1(string haystack, string needle) {
		if (needle.size() == 0) return 0;
		int size = needle.size();
		int* p = new int[size];
		//int next[needle.size()];
		getnext(p, needle);
		int j = -1;
		for (int i = 0; i < haystack.size(); i++) {
			while (j >= 0 && haystack[i] != needle[j+1]) {
				j = p[j];
			}
			if (haystack[i] == needle[j+1])
			{
				j++;
			}
			if (j == needle.size()-1) {
				return (i - needle.size() + 1);
			}
		}
		return -1;
	}

};



void main() 
{
	string hay, need;
	hay = "helloeeessaabaabaafdas";
	need = "aabaaf" ;
	Solution s;
	cout<<s.strStr(hay,need)<<endl;
	cout << s.strStr1(hay, need) << endl;
	system("pause");

}