3. Longest Substring Without Repeating Characters

Given a string, find the length of the longest substring without repeating characters.

Examples:

Given "abcabcbb", the answer is "abc", which the length is 3.

Given "bbbbb", the answer is "b", with the length of 1.

Given "pwwkew", the answer is "wke", with the length of 3. Note that the answer must be a substring, "pwke" is a subsequence and not a substring.

public class Solution {
    public int lengthOfLongestSubstring(String s) {
        int dp[] = new int[128]; //indicated the latest appearance of 128 ASCII letter
        int start = 0; //start position of current traverse
        int maxLength = 0;
        int curLength = 0;
        for(int i = 0; i < dp.length; i++){ //不能使用int i:a, 因为遍历的i会被改变值
            dp[i] = -1; //initialized as -1
        }
        
        for(int i = 0; i < s.length(); i++){
            if(dp[s.charAt(i)] < start) { //haven't repeated in the current traverse
                dp[s.charAt(i)]=i;
            }
            else{ //repeat occurs
                if(i-start > maxLength){
                    maxLength = i-start;
                }
                //reset
                start = dp[s.charAt(i)]+1;
                dp[s.charAt(i)] = i;
            }
        }
        
        if(s.length()-start > maxLength){ //final traverse substring
            maxLength = s.length()-start;
        }
        return maxLength;
    }
}