28. Find the Index of the First Occurrence in a String
題目 :
給2個字串needle和haystack，
回傳needle第一次出現在haystack中的index，
如果needle不在haystack中則回傳-1
Example 1:
Input: haystack = "sadbutsad", needle = "sad"
Output: 0
Explanation: "sad" occurs at index 0 and 6.
The first occurrence is at index 0, so we return 0.
Example 2:
Input: haystack = "leetcode", needle = "leeto"
Output: -1
Explanation: "leeto" did not occur in "leetcode", so we return -1.
思路 :
for迴圈跑haystack
找到第一個字母符合的就比對一下
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python code :
class Solution:
def strStr(self, haystack: str, needle: str) -> int:
len_needle = len(needle)
for i in range(len(haystack)) :
if haystack[i] == needle[0] :
if i+len_needle-1 < len(haystack) :
if haystack[i:i+len_needle] == needle :
return i
return -1
python直接可以[i:i+長度]比對起來比較方便
其他語言應該不太能這樣寫??
但我看這題related topic有two pointer
不過不太懂要怎麼用two pointer
有大師要解惑嗎??