String总结

3. Longest Substring Without Repeating Characters

这道题就是用一个Dict来统计字符所出现的index,然后不断计算不重复字符串的长度

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
class Solution(object):
def lengthOfLongestSubstring(self, s):
"""
:type s: str
:rtype: int
"""
useddict = {}
maxnum,start = 0,0
for i in range(len(s)):
if s[i] in useddict and start <= useddict[s[i]]:
start = useddict[s[i]] + 1
else:
maxnum = max(maxnum, i - start + 1)

useddict[s[i]]= i
return maxnum

76. Minimum Window Substring

这题和之前的非常像,就是需要处理的边界条件很多

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
from collections import defaultdict
class Solution(object):
def minWindow(self, s, t):
"""
:type s: str
:type t: str
:rtype: str
"""
if not s:
return ""
if not t:
return ""
useddict = defaultdict(int)
for char in t:
useddict[char] += 1
length = len(t)
minnum,start,end = len(s)+1,0,0
head = 0
for i in range(len(s)):
if s[i] in useddict:
useddict[s[i]] -= 1
if useddict[s[i]]>=0:
length -= 1
while length==0:
if i - start+1 < minnum:
minnum = i-start+1
head = start
if s[start] in useddict:
useddict[s[start]] += 1
if useddict[s[start]] > 0: ## more same char was used
length += 1
start += 1


return s[head:head+minnum] if minnum <= len(s) else ""
Donate comment here