[LintCode] Longest Substring Without Repeating Characters

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

Have you met this question in a real interview? 

Yes

Example

For example, the longest substring without repeating letters for"abcabcbb" is "abc", which the length is 3.

For "bbbbb" the longest substring is "b", with the length of 1.

Challenge 

O(n) time

LeetCode上的原题，请参见我之前的博客Longest Substring Without Repeating Characters。

解法一：

class Solution {
public:
    /**
     * @param s: a string
     * @return: an integer 
     */
    int lengthOfLongestSubstring(string s) {
        int res = 0, left = -1;
        vector<int> m(256, -1);
        for (int i = 0; i < s.size(); ++i) {
            left = max(left, m[s[i]]);
            m[s[i]] = i;
            res = max(res, i - left);
        }
        return res;
    }
};

解法二：

class Solution {
public:
    /**
     * @param s: a string
     * @return: an integer 
     */
    int lengthOfLongestSubstring(string s) {
        int res = 0, left = 0, right = 0;
        unordered_set<char> st;
        while (right < s.size()) {
            if (!st.count(s[right])) {
                st.insert(s[right++]);
                res = max(res, (int)st.size());
            } else {
                st.erase(s[left++]);
            }
        }
        return res;
    }
};