Longest_Substring.java

// Question 

// 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 

// *****************************************************************************************************


// Solution

public class Longest Substring {
    public int lengthOfLongestSubstring(String s) {
        int len = s.length();
        int ans=0;
        Map<Character,Integer> map = new HashMap<>();
        for(int j=0, i=0; j<len; j++){
            if(map.containsKey(s.charAt(j)))
                i = .max(map.get(s.charAt(j)), i);
            ans = .max(ans, j-i+1);
            map.put(s.charAt(j), j+1);
        }
        return ans;
    }   
}

// Time Complexity = O(n)
// Space Complexity = O(n)