28. 找出字符串中第一个匹配项的下标
O(m+n)
最长相同的前后缀的长度
跳转到next的长度下标位置
创建next数组
- 初始化
- 遍历
- 前后缀相同
- 前后缀不同
- 更新next
def strStr(self, haystack: str, needle: str) -> int:
next = [0] * len(needle)
# create the next arr
# suffix
j = 1
# prefix
i = 0
while j < len(needle):
# if not
while i > 0 and needle[i] != needle[j]:
i = next[i-1]
# if matched
if needle[i] == needle[j]:
i += 1
next[j] = i
j += 1
if len(needle) == 0:
return 0
j = 0
for i in range(len(haystack)):
while j >= 1 and haystack[i] != needle[j]:
j = next[j-1]
if haystack[i] == needle[j]:
j += 1
if j == len(needle):
return i - len(needle) + 1
return -1
459. 重复的子字符串
用KMP的思路
def repeatedSubstringPattern(self, s: str) -> bool:
next = [0] * len(s)
if len(s) == 1:
return False
# create the next arr
# suffix
j = 1
# prefix
i = 0
while j < len(s):
# if not
while i > 0 and s[i] != s[j]:
i = next[i-1]
# if matched
if s[i] == s[j]:
i += 1
next[j] = i
j += 1
return next[-1] != 0 and len(s) % (len(s) - next[-1]) == 0
方法
- 双指针
- 反转
- KMP
