[LeetCode] 3. Longest Substring Without Repeating Characters

最新推荐文章于 2021-12-03 15:58:56 发布

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本文探讨了如何在给定字符串中找到最长的无重复字符子串，通过三个实例展示了算法的应用，例如输入abcabcbb，输出为3，最长无重复子串为abc。文章提供了一种C++实现方案，利用哈希表跟踪字符位置，以O(n)的时间复杂度高效解决问题。

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.

C++ 解法一：

class Solution {
public:
    int lengthOfLongestSubstring(string s) {
        int res = 0, left = -1, n = s.size();
        unordered_map<int, int> m;
        for (int i = 0; i < n; ++i) {
            if (m.count(s[i]) && m[s[i]] > left) {
                left = m[s[i]];  
            }
            m[s[i]] = i;
            res = max(res, i - left);            
        }
        return res;
    }
};