LeetCode 3: Longest Substring Without Repeating Characters

Difficulty: 3

Frequency: 2

Problem:

Given a string, find the length of the longest substring without repeating characters. For example, the
longest substring without repeating letters for "abcabcbb" is "abc", which the length is 3. For "bbbbb" the longest substring is "b", with the length of 1.

Solution:

class Solution {
public:
int lengthOfLongestSubstring(string s) {
// Start typing your C/C++ solution below
// DO NOT write int main() function
int i_max_length = 0, i_max_length_from_end = 0;
int p_last_index[26];
memset(p_last_index, 0xFF, sizeof(int)*26);
for (int i = 0; i<s.size(); i++)
{
if (p_last_index[s[i]-'a']==-1||(i-p_last_index[s[i]-'a'])>i_max_length_from_end)
{
p_last_index[s[i]-'a'] = i;
i_max_length_from_end++;
i_max_length = i_max_length>i_max_length_from_end?i_max_length:i_max_length_from_end;
}
else
{
i_max_length_from_end = i - p_last_index[s[i]-'a'];
p_last_index[s[i]-'a'] = i;
}
}
return i_max_length;
}
};
Notes:
Time complexity O(n).