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Leetcode经典试题：Longest Substring Without Repeating Characters解析

题目如下：

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

我学习的优秀代码：

int lengthOfLongestSubstring(string s) {
        vector<int> dict(256, -1);
        int maxLen = 0, start = -1;
        for (int i = 0; i != s.length(); i++) {
            if (dict[s[i]] > start)
                start = dict[s[i]];
            dict[s[i]] = i;
            maxLen = max(maxLen, i - start);
        }
        return maxLen;
    }

来源：https://leetcode.com/problems/longest-substring-without-repeating-characters/discuss/1737/C%2B%2B-code-in-9-lines.

个人加英文注释版：

class Solution {
public:
    int lengthOfLongestSubstring(string s) {
        vector<int> dict(256,-1);//256 is the amount of ASCII and its expanding. use -1 to initialize,dict stores each letter's  index of their last position
        int length=0,start=-1;//initialize
        for(int i=0;i<s.length();i++){// i is the index
            if(dict[s[i]]>start)// it means whether this letter is already contained in the choosed string
                start=dict[s[i]];// if true, the index of start should be reset to the index of the repeated word
            dict[s[i]]=i;//update the index of their last position
            length=max(length,i-start);//i and start both point at the same letter, so the real length is one letter less,i-start-1+1=i-start
        }
        return length;//return the largest length
    }
};

解析如下{