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3. Longest Substring Without Repeating Characters 👍

Longest Substring with At Most Two Distinct Characters | Longest Substring with At Most K Distinct Characters | Subarrays with K Different Integers | Maximum Erasure Value | Number of Equal Count Substrings | Minimum Consecutive Cards to Pick Up | Longest Nice Subarray | Optimal Partition of String

Problem

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

  • 0 <= s.length <= 5 * 104

  • s consists of English letters, digits, symbols and spaces.

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

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

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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.

Complexity:

  • Time complexity : O(n).
  • Space complexity : O(n).

Solution

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class Solution {
 public:
  int lengthOfLongestSubstring(string s) {
    int ans = 0;
    vector<int> count(128);

    for (int l = 0, r = 0; r < s.length(); ++r) {
      ++count[s[r]];
      while (count[s[r]] > 1)
        --count[s[l++]];
      ans = max(ans, r - l + 1);
    }

    return ans;
  }
};

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class Solution {
  public int lengthOfLongestSubstring(String s) {
    int ans = 0;
    int[] count = new int[128];

    for (int l = 0, r = 0; r < s.length(); ++r) {
      ++count[s.charAt(r)];
      while (count[s.charAt(r)] > 1)
        --count[s.charAt(l++)];
      ans = Math.max(ans, r - l + 1);
    }

    return ans;
  }
}

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class Solution:
  def lengthOfLongestSubstring(self, s: str) -> int:
    ans = 0
    count = collections.Counter()

    l = 0
    for r, c in enumerate(s):
      count[c] += 1
      while count[c] > 1:
        count[s[l]] -= 1
        l += 1
      ans = max(ans, r - l + 1)

    return ans