LeetCode: Longest Substring Without Repeating Characters (3)

最长无重复子串算法

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#最长不重复子串

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本文介绍了一种求解最长无重复字符子串长度的方法，通过遍历字符串并使用哈希表记录每个字符的位置，有效地找到最长无重复子串。讨论了算法实现细节及时间复杂度。

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：求最长不重复子字符串类问题，可以将字符串按照顺序存放在连续的数组中即可。在存入的时候判断是否重复，做香烟处理。遍历一次即可得到最长子串。时间复杂度：O（n）

扩展：求最长重复子字符串

#define max(x,y) (x>y)?(x):(y)
class Solution {
public:
    int lengthOfLongestSubstring(string s) {
        vector<int> hash(256,-1);
        int sMax = 0;
        int latestStart = 0;
        int start       =0;
        
        for(int i= 0;i<s.length();i++)
        {
            //repeat char
            if(hash[s[i]]!= -1)
            {
                sMax = max(sMax,i-start);
                latestStart = start;
                start = hash[s[i]]+1;
                for(int j = latestStart;j<start;j++)
                    hash[s[j]] = -1;
            }
            hash[s[i]] = i;
        }
        return max(sMax,s.length()-start);
    }
};