LeetCode 3：Longest Substring Without Repeating Characters（无重复字符的最长子串）

题目：

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.

代码：

class Solution {
public:
    int lengthOfLongestSubstring(string s) {
        int l = 0 , h = 0;
        int result = 0;
        int cal[256] = {0};
        while( h < s.size() ){
            int len = 0;
            cal[s[h]] ++;
            while( cal[s[h]] > 1 ){   // if cal[s[h]] > 1 , we can judge that s[h] appears more than one between s[l] to s[h]
                cal[s[l]]--;          // increase l by one , cal[s[l]] will be reduced until s[h] == 1 . 
                ++ l;                 // it means that s[h] appears once between s[l] to s[h]
            }
            result = max( result , h - l + 1 );
            ++ h;
        }
        return result;
    }
};