[Leetcode] Longest substring without repeating characters

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.

Https://oj.leetcode.com/problems/longest-substring-without-repeating-characters/

 

Idea: use an exist array to save whether or not the characters appear (assuming that char set is ASCII) and traverse the array from front to back. If an existing character exists, it should be rolled back to the next position where the character appeared last time to start statistics (for example), and pay attention to the simultaneous update of the exist array.

 

public class Solution {    public int lengthOfLongestSubstring(String s) {        if (s == null || s.length() == 0)            return 0;        int res = 1;        boolean[] exist = new boolean[256];        int start = 0;        for (int i = 0; i < s.length(); i++) {            char ch = s.charAt(i);            if (exist[ch]) {                res = Math.max(res, i - start);                for (int k = start; k < i; k++) {                    if (s.charAt(k) == ch) {                        start = k + 1;                        break;                    }                    exist[s.charAt(k)] = false;                }            } else                exist[ch] = true;        }        res = Math.max(res, s.length() - start);        return res;    }    public static void main(String[] args) {        System.out.println(new Solution().lengthOfLongestSubstring("abcabcbb"));        System.out.println(new Solution().lengthOfLongestSubstring("bbbbb"));        System.out.println(new Solution()                .lengthOfLongestSubstring("fpdcztbudxfipowpnamsrfgexjlbjrfoglthewbhtiriznzmolehqnlpwxrfowwwjrd"));    }}

 

 

 

Refer:

Http://blog.csdn.net/likecool21/article/details/10858799

Http://www.programcreek.com/2013/02/leetcode-longest-substring-without-repeating-characters-java/