3. Longest Substring Without Repeating Characters， leetcode

题目：

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

Examples:

Given "abcabcbb", the answer is "abc", which the length is 3.

Given "bbbbb", the answer is "b", with the length of 1.

Given "pwwkew", 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.

思路和代码

class Solution {public:    int lengthOfLongestSubstring(string s) {unordered_map<char, int> hash;//这里哈希表可以换为 vector<>, vector的下标就是哈希表里的key；因为这道题目的key足够小 所以 hash表问题可以转化为数组问题int ans = 0;int l = -1;for (int r = 0; r < s.size(); r++){if (hash.find(s[r]) != hash.end()){l = max(l, hash[s[r]]);//重点！！ 这里左指针不能减小}hash[s[r]] = r;ans = max(ans, r - l);}return ans;}};

总结：

这里哈希表可以换为 vector<>, vector的下标就是哈希表里的key；因为这道题目的key足够小 所以 hash表问题可以转化为数组问题