20240305-Day 25-点亮代码技能

Leetcode28（找出字符串中第一个匹配项的下标）

C++：

KMP算法的应用，算法讲解在这里

class Solution {
public:
    int strStr(string haystack, string needle) {
        int l = haystack.size();
        int next[needle.size()];
        get_next(next, needle);
        int j = 0;
        for(int i = 0; i < l; i++)
        {
            while(j > 0 && haystack[i] != needle[j])
                j = next[j-1];
            if(haystack[i] == needle[j])
                j++;
            if(j == needle.size())
                return i-needle.size()+1;
        }
        return -1;
    }
    //找到next数组
    void get_next(int *next, const string &s)
    {
        next[0] = 0;
        int j = 0;
        for(int i = 1; i < s.size(); i++)
        {
            while(j > 0 && s[i] != s[j])
                j = next[j-1];
            if(s[i] == s[j])
                j++;
            next[i] = j;
        }
    }
};

Python：

class Solution:
    def strStr(self, haystack: str, needle: str) -> int:
        # 找出next数组
        nxt = [0] * len(needle)
        j = 0
        for i in range(1, len(needle)):
            while j > 0 and needle[i] != needle[j]:
                j = nxt[j-1]
            if needle[i] == needle[j]:
                j += 1
            nxt[i] = j
        
        # 利用next数组查找重复字符
        m = 0
        for n in range(len(haystack)):
            while m > 0 and haystack[n] != needle[m]:
                m = nxt[m-1]
            if haystack[n] == needle[m]:
                m += 1
            if m == len(needle):
                return n-m+1
        return -1

原文地址：https://blog.csdn.net/qq_43487696/article/details/136472706

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