【LeetCode】3. Longest Substring Without Repeating Characters

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3.Longest Substring Without Repeating Characters

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

没有重复字符的最长子串

使用map来存储字符串以及对应的索引，建立一张索引表。以起点start开始查找，若无重复字符，则maxlen = i-start

abcabcbb
^  ^
s  i

当字符查表已存在，更新起点start为当前字符索引

Solution

class Solution {
public:
    int lengthOfLongestSubstring(string s) {
        unordered_map<char,int> char_map;
        int maxlen= 0;
        int start = -1;
        for(int i = 0; i<s.length();i++){
            if(char_map.count(s[i])!=0){
                start = max(start,char_map[s[i]]);
            }
            char_map[s[i]]=i;
            maxlen = max(maxlen,i-start);
        }
        return maxlen;
    }
};