Leetcode03

Longest Substring Without Repeating Characters:
Given a string, find the length of the longest substring without repeating characters.
Example 1:
Input: “abcabcbb”
Output: 3
Explanation: The answer is “abc”, which the length is 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.

Solution:

#include <iostream>
#include <vector>

using namespace std;

// 时间复杂度：o（n）
// 空间复杂度：o（1）
// 用了滑动窗口的思想，在滑动窗口中判断是否有重复
class Solution{
public:
    int lengthOfLongestSubstring(string s) {

        int freq[256] = {0}; // 检测滑动窗口中是否有重复
        int l = 0, r = -1;   // 滑动窗口为s[l...r]
        int res = 0;

        while (l < s.size() ){

            if (r + 1 < s.size() && freq[s[r+1]] == 0) {
                r ++;
                freq[s[r]] ++;
            } else {
                freq[s[l]] --;
                l++;
            }

            res = max(res, r - l + 1);
        }

        return res;
    }
};

int main(){

    return 0;
}