28_ImplementstrStr.md

28. Implement strStr()

Implement strStr().

Given two strings needle and haystack, return the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.

Clarification:

What should we return when needle is an empty string? This is a great question to ask during an interview.

For the purpose of this problem, we will return 0 when needle is an empty string. This is consistent to C's strstr() and Java's indexOf().

Example 1:

Input: haystack = "hello", needle = "ll"
Output: 2

Example 2:

Input: haystack = "aaaaa", needle = "bba"
Output: -1

Clarification:

1 <= haystack.length, needle.length <= 104
haystack and needle consist of only lowercase English characters.

Solution:

• 解法一
  • 使用find method
• 解法二
  1. 基本檢核
  2. 從頭開始直接比對needle在目標字串是否相似

code:

• python

  class Solution:
       # 解法一
      def strStr(self, haystack: str, needle: str) -> int:
          return haystack.find(needle)
      # 解法二
      def strStr(self, haystack: str, needle: str) -> int:
          if len(needle) == 0:
              return 0
          for i in range(len(haystack)):
              if haystack[i:i+len(needle)] == needle:
                  return i
          return -1