3. Longest Substring Without Repeating Characters

Problem:

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.

思路：

Solution (C++):

int lengthOfLongestSubstring(string s) {
    int n = s.length();
    if (n == 0)  return 0;
    int pre = -1, cur_len = 0, len = 0;
    unordered_map<char, int> map;
    for (auto c : s)  map[c] = -1;
    
    for (int i = 0; i < n; ++i) {
        pre = max(pre, map[s[i]]);
        cur_len = i - pre;
        len = max(len, cur_len);
        map[s[i]] = i;
    }
    return len;
}

性能：

Runtime: 32 ms  Memory Usage: 8.7 MB

思路：

Solution (C++):

int lengthOfLongestSubstring(string s) {
    int n = s.length();
    if (n == 0)  return 0;
    unordered_map<char, int> map;
    int len = 0, last_len = 0;
    for (auto c : s)  map[c] = -1;
    
    for (int i = 0; i < n; ++i) {
        if (i - map[s[i]] <= last_len)
            last_len = i - map[s[i]];
        else 
            ++last_len;
        map[s[i]] = i;
        len = max(len, last_len);
    }
    return len;
}

性能：

Runtime: 32 ms  Memory Usage: 8.6 MB