3. Longest Substring Without Repeating Characters

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

Example 1:
Input: "abcabcbb"
Output: 3
Explanation: The answer is "abc", with the length of 3.

Example 2:
Input: "bbbbb"
Output: 1
Explanation: The answer is "b", with the length of 1.

Example 3:
Input: "pwwkew"
Output: 3
Explanation: 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.

难度：medium

题目：
给定一字符串，找出最长且无重复字符的子串。

思路：

1. 创建字符下标数组用以记录访问过的字符串中的字符。下标由1开始，用以区别数组的初始化值0.
2. 定义子串的起始下标，子串的窗口为[begin indx, i]

Runtime: 19 ms, faster than 96.64% of Java online submissions for Longest Substring Without Repeating Characters.

class Solution {
    public int lengthOfLongestSubstring(String s) {
        if (null == s || "" == s) {
            return 0;
        }
        
        int[] charIdxArray = new int[256];
        int maxLen = 0;
        int beginIdx = 0;
        for (int i = 0; i < s.length(); i++) {
            char c = s.charAt(i);
            int idx = charIdxArray[c];
            if (idx < 1 || idx <= beginIdx) {
                charIdxArray[c] = i + 1;
            } else {
                beginIdx = idx;
                charIdxArray[c] = i + 1;
            }
            maxLen = Math.max(maxLen, i + 1 - beginIdx);
        }
        
        return maxLen;
    }
}