Longest Substring Without Repeating Characters
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题目:https://leetcode.com/problems/longest-substring-without-repeating-characters/
算法思路:
定义三个变量positions、max、start,分别表示不同字符的位置、最大不重复子串长度、不重复子串的开始位置
不重复子串的最大长度是当前max的值与当前遍历位置减去start之间的较大者。
start记录的位置,表示了当前位置和start之间不存在重复字符,一旦遇到重复字符,就需要更新start。所以,程序始终保持,start与当前位置之间字符的不重复性。start的更新:
在字符串遍历过程中,如果整个遍历都没有重复字符,则最大不重复子串长度就是字符串遍历的最后位置减去start(不重复子串开始位置)。如果在遍历过程中出现了重复字符,则需要更新start,start就等于该重复字符上一次出现的位置。
positions的更新:
遍历过程中,对于每一个字符,都将当前位置覆盖之前字符出现的位置。
max的更新:
每遍历一个字符,都需要重新计算max,比较当前max和当前位置与start之差的大小,用较大的更新max
class Solution(object): def lengthOfLongestSubstring(self, s): """ :type s: str :rtype: int """ positions = {} max = 0 start = -1 for index, str in enumerate(s): if str in positions and start < positions[str]: start = positions[str] if max < index - start: max = index - start positions[str] = index return max
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