Added question description and comments to the code.

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.

Author: nidhisethi88

Strings/length_of_longest_substring_without_repeat_char.cpp

@@ -0,0 +1,19 @@
+int lengthOfLongestSubstring(string s) {
+        if(s.length()<=1)
+            return s.length();
+        vector<int> freq(128,0);
+        int si=0,ei=0,n=s.length(),maxlen=INT_MIN,count=0;
+        while(ei<n){
+            if(freq[s[ei++]]++ > 0)
+                count++;
+            
+            while(count>0){                 //if freq of char at ei in the chosen substring is greater than 2
+                if(freq[s[si++]]-- >1)    //iterate till the freq becomes 1
+                    count--;
+            }
+            
+            if(ei-si>maxlen)                //each time compare length of obtained substr with unique char to the maximum length
+                maxlen=ei-si;
+        }
+        return maxlen;
+    }