LongestSubstring.java

import java.util.*;

/**
 * Given a string, find the length of the longest substring without repeating
 * characters. For example, the longest substring without repeating letters for
 * "abcabcbb" is "abc", which the length is 3. For "bbbbb" the longest
 * substring is "b", with the length of 1.
 * 
 * Tags: Hashtable, Two pointers, String
 */
class LongestSubstring {
    public static void main(String[] args) {
        // System.out.println(lengthOfLongestSubstring("abcabcbb"));
        // System.out.println(lengthOfLongestSubstring("bbbbb"));
        // System.out.println(lengthOfLongestSubstring(""));
        // System.out.println(lengthOfLongestSubstring("fdjskajfhh"));
        // System.out.println(lengthOfLongestSubstring("iiiiiiioooooooooooooo"));
        // System.out.println(lengthOfLongestSubstring("aeiou"));
        System.out.println(lengthOfLongestSubstring("hnwnkuewhsqmgbbuqcljjivswmdkqtbxixmvtrrbljptnsnfwzqfjmafadrrwsofsbcnuvqhffbsaqxwpqcac"));
    }
    
    /**
     * Traverse the string
     * Get current character
     * Update start point
     * Update max
     * Put current char in map
     */
    public static int lengthOfLongestSubstring(String s) {
        if (s == null || s.length() == 0) return 0;
        
        Map<Character, Integer> map = new HashMap<Character, Integer>();
        int start = 0;
        int max = 0;
        
        for (int i = 0; i < s.length(); i++) {
            char c = s.charAt(i);
            /*start point can be recent dup's next char or last start*/
            start = Math.max(start, (map.containsKey(c)) ? map.get(c) + 1 : 0);
            /*if current str len is bigger then update*/
            max = Math.max(max, i - start + 1);
            /*add char to map with index*/
            map.put(c, i);
        }
        return max;
    }
}