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Longest Substring with Non-repeating Characters

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Hustler answered on February 17, 2022 Popularity 5/10 Helpfulness 1/10

answer Longest Substring with Non-repeating Characters

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Longest Substring with Non-repeating Characters

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Longest Substring Without Repeating Characters
Problem Statement
Given a string s, find the length of the longest substring without repeating characters.   

Example
Input: s = "abcabcbb"
Output: 3
Explanation: The answer is "abc", with the length of   
 3.
Approach: Sliding Window
A common and efficient approach to solve this problem is using the sliding window technique.

Initialize two pointers: left and right to mark the beginning and end of the sliding window respectively.
Maintain a set: to store unique characters encountered in the current window.
Iterate through the string:
If the current character is not in the set, expand the right pointer and add the character to the set.
If the current character is already in the set, it means we have a repeated character. Shrink the left pointer until the repeated character is removed from the window.
Update the maximum length of the substring found so far.
Python Implementation
Python
def lengthOfLongestSubstring(s: str) -> int:
    char_set = set()
    left = right = 0
    max_length = 0

    while right < len(s):
        if s[right] not in char_set:
            char_set.add(s[right])
            max_length = max(max_length, right - left + 1)
            right += 1
        else:
            char_set.remove(s[left])
            left += 1

    return max_length   

Use code with caution.

Explanation
The char_set is used to keep track of unique characters in the current window.
The left and right pointers define the sliding window.
The max_length variable keeps track of the maximum length found so far.
We iterate through the string, expanding the window if the character is new, and shrinking it otherwise.
Time and Space Complexity
Time complexity: O(n) where n is the length of the string.
Space complexity: O(n) in the worst case when all characters are unique.

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Contributed on Aug 02 2024

Hustler

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Longest Substring Without Repeating Characters

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/*
    Javascript Solution - With Better Performance
    Methods used in this algorithm are:
    1. Two Pointer Technique
    2. Sliding Window Technique
    3. Hash Map

    Time complexity: O(N)
    Space complexity: O(N),
    If the string does not contain repeated characters, 
    then the hash map will contain N characters.
*/

const s = "sdtvtsgh"

const lengthOfLongestSubstring = function(s) {
    let max_length = 0
    let map = {}
    let l = 0

    for (let r = 0; r < s.length; r++) {
        if (map.hasOwnProperty(s[r])) {
            const collision_index = map[s[r]]

            if (collision_index >= l) {
                l = collision_index + 1
            }

            delete map[s[collision_index]]
        }

        if (!map.hasOwnProperty(s[r])) {
            map[s[r]] = r
        }

        if (max_length < (r + 1) - l) {
            max_length = (r + 1) - l
        }

        console.log(map, ':   (', r + 1, '-', l, ')')
    }

    return max_length
}


console.log(lengthOfLongestSubstring(s))

// [Log]:
{ s: 0 } :   ( 1 - 0 )
{ s: 0, d: 1 } :   ( 2 - 0 )
{ s: 0, d: 1, t: 2 } :   ( 3 - 0 )
{ s: 0, d: 1, t: 2, v: 3 } :   ( 4 - 0 )
{ s: 0, d: 1, v: 3, t: 4 } :   ( 5 - 3 )
{ d: 1, v: 3, t: 4, s: 5 } :   ( 6 - 3 )
{ d: 1, v: 3, t: 4, s: 5, g: 6 } :   ( 7 - 3 )
{ d: 1, v: 3, t: 4, s: 5, g: 6, h: 7 } :   ( 8 - 3 )

max_length = 5

Popularity 10/10 Helpfulness 3/10 Language javascript

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Tags: javascript j

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Contributed on Aug 21 2022

Mysterious Macaque

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longest substring without repeating characters

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/**
 * @param {string} s
 * @return {number}
 */
var lengthOfLongestSubstring = function(s) {
    if (!s.length) return 0

    let left = 0, right = 0
    let maxLength = -Infinity
    const hashSet = {}
    const len = s.length

    while(right < len){
        if (hashSet.hasOwnProperty(s[right])){
            if (hashSet[s[right]] >= left){
                left = hashSet[s[right]]+1
            }
        }
            const lenn = right-left+1
            maxLength = Math.max(lenn, maxLength)
            hashSet[s[right]] = right
            right++
        
    }
    return maxLength

};

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Source: leetcode.com

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Contributed on Jul 31 2024

Adventurous Alligator

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longest substring without repeating characters

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// JavaScript Solution - Credit to @albertchanged on LC
// Sliding window implementation
var lengthOfLongestSubstring = function(s) {
  if (!s.length) return 0;
  
  let left = 0, right = 0;
  let maxLength = -Infinity;
  const set = new Set();

  while (right < s.length) {
    // If s[right] has not been seen yet
    if (!set.has(s[right])) {
      // Add it to the set
      set.add(s[right]);
      // Increase size of window to right
      right++;
      // Update maxLength; set size represents length of unique substring
      maxLength = Math.max(maxLength, set.size);
    } else {
      // We've seen s[right] so we need to shrink the window
      // Delete s[left] from set
      set.delete(s[left]);
      // Shrink window from left
      left++;
    }
  }

  return maxLength;
}

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Tags: javascript j

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Contributed on Aug 21 2022

Ryan Garcia

0 Answers Avg Quality 2/10

3. Longest Substring Without Repeating Characters

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import java.io.*;
 
class GFG {
    public static int longestUniqueSubsttr(String str)
    {
        String test = "";
 
        // Result
        int maxLength = -1;
 
        // Return zero if string is empty
        if (str.isEmpty()) {
            return 0;
        }
        // Return one if string length is one
        else if (str.length() == 1) {
            return 1;
        }
        for (char c : str.toCharArray()) {
            String current = String.valueOf(c);
 
            // If string already contains the character
            // Then substring after repeating character
            if (test.contains(current)) {
                test = test.substring(test.indexOf(current)
                                      + 1);
            }
            test = test + String.valueOf(c);
            maxLength = Math.max(test.length(), maxLength);
        }
 
        return maxLength;
    }
 
    // Driver code
    public static void main(String[] args)
    {
        String str = "geeksforgeeks";
        System.out.println("The input string is " + str);
 
        int len = longestUniqueSubsttr(str);
        System.out.println("The length of the longest "
                           + "non-repeating character "
                           + "substring is " + len);
    }
}
 
// This code is contributed by Alex Bennet

Popularity 10/10 Helpfulness 3/10 Language java

Source: www.geeksforgeeks.org

Tags: java

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Contributed on Feb 17 2022

Manav Sarkar

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longest substring without repeating characters

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class Solution {
    public int lengthOfLongestSubstring(String s) {int max=0;
        HashMap<Character,Integer>hm=new HashMap<>();
        for(int i=0,j=0;i<s.length();i++){
            if(hm.containsKey(s.charAt(i))){
                j=Math.max(j,hm.get(s.charAt(i))+1);
            }
            hm.put(s.charAt(i),i);
            max=Math.max(max,i-j+1);
        }
        return max;
        
    }
}

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Contributed on Aug 22 2022

Nasty Nightingale

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longest substring without repeating characters

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public class Solution 
{
    public int LengthOfLongestSubstring(string str) 
    {
        var dict = new Dictionary<char, int>();
        var max = 0;
        int start = 0;
        for (int i = 0; i < str.Length; i++)
        {
            var x = str[i];
            if (!dict.ContainsKey(x))
            {
                dict.Add(x, 1);
            }
            else
            {
                dict[x] += 1;
                while (start <= i && dict.ContainsKey(str[start]) && dict[x] > 1)
                {
                    dict[str[start]]--;
                    if (dict[str[start]] == 0)
                        dict.Remove(str[start]);
                    start++;
                }
            }
            max = Math.Max(max, i - start + 1);
        }
        return max;
    }
}

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Source: leetcode.com

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Contributed on Jun 10 2022

PrashantUnity

0 Answers Avg Quality 2/10

Longest Substring Without Repeating Characters

Comment

/*
  Given a string s, find the length of the longest substring (A substring is 
  a contiguous non-empty sequence of characters within a string.) 
  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.
*/

   const longestStr = s => {
    if(s.length < 2) return s.length

    let [left, right, partial, curIdx, finalLength] = 
        [0, s.length, new Set(), 0, -Infinity]

    while (left < right) {
        partial.add(s[left])

        const curChar = s[left+1]

        // Base case to exit loop early
        if (finalLength > (right - curIdx)) break

        if (partial.has(curChar)) {
            curIdx += 1
            left = curIdx

            partial.size > finalLength ? finalLength = partial.size : null
            partial.clear()
        }else left++

        left === right ? partial.size > finalLength ? 
          finalLength = partial.size : null : null

    }

    return finalLength
  }

  const s = "abcabcbb" // 3
  const res = longestStr(s)
  console.log(res)
    
  /*
	Time Complexity: O(n) (average case)
	Space Complexity: O(n)  
  */

// With love @kouqhar

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Contributed on Nov 07 2024

kouqhar

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Longest Substring Without Repeating Characters

Comment

class Solution {

    /**
     * @param String $s
     * @return Integer
     */
    function lengthOfLongestSubstring($s) {
        
    }
}

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Tags: longest-substring longest-substrin

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Contributed on Aug 17 2022

CodeBlack reactor

0 Answers Avg Quality 2/10

find longest substring without repeating characters

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One thing needs to be mentioned is that when asked to find maximum substring, we should update maximum after the inner while loop to guarantee that the substring is valid. On the other hand, when asked to find minimum substring, we should update minimum inside the inner while loop.

The code of solving Longest Substring with At Most Two Distinct Characters is below:

int lengthOfLongestSubstringTwoDistinct(string s) {
        vector<int> map(128, 0);
        int counter=0, begin=0, end=0, d=0; 
        while(end<s.size()){
            if(map[s[end++]]++==0) counter++;
            while(counter>2) if(map[s[begin++]]--==1) counter--;
            d=max(d, end-begin);
        }
        return d;
    }
The code of solving Longest Substring Without Repeating Characters is below:

Update 01.04.2016, thanks @weiyi3 for advise.

int lengthOfLongestSubstring(string s) {
        vector<int> map(128,0);
        int counter=0, begin=0, end=0, d=0; 
        while(end<s.size()){
            if(map[s[end++]]++>0) counter++; 
            while(counter>0) if(map[s[begin++]]-->1) counter--;
            d=max(d, end-begin); //while valid, update d
        }
        return d;
    }
I think this post deserves some upvotes! : )

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Contributed on Oct 22 2022

Prathz SHAH

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Longest Substring Without Repeating Characters

Comment

class Solution {
public:
    int lengthOfLongestSubstring(string s) {
        
    }
};

Popularity 9/10 Helpfulness 1/10 Language cpp

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Tags: c++ longest-substring longest-subs

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Contributed on Aug 17 2022

CodeBlack reactor

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Longest Substring with Non-repeating Characters

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Longest Substring Without Repeating Characters

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