Longest Substring Without Repeating Characters.cpp

/*
Longest Substring Without Repeating Characters
==============================================

Given a string s, find the length of the longest substring without repeating characters.

Example 1:
Input: s = "abcabcbb"
Output: 3
Explanation: The answer is "abc", with the length of 3.

Example 2:
Input: s = "bbbbb"
Output: 1
Explanation: The answer is "b", with the length of 1.

Example 3:
Input: s = "pwwkew"
Output: 3
Explanation: The answer is "wke", with the length of 3.
Notice that the answer must be a substring, "pwke" is a subsequence and not a substring.

Example 4:
Input: s = ""
Output: 0

Constraints:
0 <= s.length <= 5 * 104
s consists of English letters, digits, symbols and spaces.
*/

class Solution
{
public:
  int lengthOfLongestSubstring(string s)
  {
    int i = 0, j = 0;
    int n = s.size(), ans = 0;

    vector<int> freq(256, 0);
    while (i < n && j < n)
    {
      while (freq[s[j]] > 0)
      {
        freq[s[i]]--;
        i++;
      }
      freq[s[j]]++;
      j++;
      ans = max(ans, j - i);
    }
    return ans;
  }
};