LeetCode_Implement strStr()

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Implement strStr()

Implement strStr(). Return the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.
（实现寻找字符串子串函数）

Example:



1. 遍历 – easy

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class Solution:
    def strStr(self, haystack, needle):
        """
        :type haystack: str
        :type needle: str
        :rtype: int
        """
        n = len(needle)
        m = len(haystack)
        
        if n == 0:
            return 0
        
        if n > m:
            return -1
        
        for i in range(m-n+1):
            if haystack[i:i+n] == needle:
                return i
        
        return -1

2. 调用 python 库函数 in, index

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class Solution:
    def strStr(self, haystack, needle):
        """
        :type haystack: str
        :type needle: str
        :rtype: int
        """
        if needle not in haystack:
            return -1
        else:
            return haystack.index(needle)