159.py

'''
Given a string, find the longest substring that contains only two unique characters. For example, given "abcbbbbcccbdddadacb", the longest substring that contains 2 unique character is "bcbbbbcccb".
'''

classSolution(object):
deflengthOfLongestSubstringTwoDistinct(self, s):
"""
 :type s: str
 :rtype: int 
 """
ifnots:
return0

unique_char, start, result= {}, 0, 0
forindex, charinenumerate(s):
ifcharinunique_char:
unique_char[s] +=1
else:
unique_char[s] =1

iflen(unique_char) <=2:
result=max(result, index-start+1)
else:
whilelen(unique_char) >2:
char_index=s[start]
count=unique_char[char_index]
ifcount==1:
delunique_char[char_index]
else:
unique_char[char_index] -=1
start+=1
returnresult