LeetcodeLongest Substring Without Repeating Characters

Posted 2020-07-17 wuezs

题目链接：https://leetcode.com/problems/longest-substring-without-repeating-characters/

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：

实质是求s内的相同字符之间的最大长度 将s将相同字符之间分割为一个个子串 比较长度，所以需要保存前面跟自己相同的字符的位置。

算法：

public int lengthOfLongestSubstring(String s) {  
    if (s == null || s.length() == 0)  
        return 0;  
  
    int max = 1;  
    int idx = -1;// 当前子串的起始位置  
    // idx取-1 是因为当字符串本身就是最长子串时 idx不会被修改 而max需要为s的长度需要加1  
    Map<String, Integer> maps = new HashMap<String, Integer>();  
    char c[] = s.toCharArray();  
  
    for (int i = 0; i < c.length; i++) {  
        if (maps.containsKey(c[i] + "") && maps.get(c[i] + "") > idx) {  
            idx = maps.get(c[i] + "");  
        }  
        max = Math.max(max, i - idx);  
        maps.put(c[i] + "", i);  
    }  
    return max;  
}