给定一个字符串，找出没有重复字符的最长子字符串的长度。

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.

解法1:

滑动窗口法，每当字符在当前窗口重复时，调整窗口大小。和最大子数组和看起来有点类似，但是思路不太一样，有机会总结一下区别。

/**
 * @param {string} s
 * @return {number}
 */
var lengthOfLongestSubstring = function(s) {
    let maxLen = 0;
    let begin = 0;
    let lastIdxOf = {};
    for (let i = 0; i < s.length; i ++) {
        let char = s.charAt(i);
        // if current char repeats in current window, adjust the window
        if (lastIdxOf[char] != null) begin = Math.max(begin, lastIdxOf[char] + 1);
        if (i - begin + 1 > maxLen) maxLen = i - begin + 1;
        lastIdxOf[char] = i;
    }
    
    return maxLen;
};