leetcode : Longest Substring Without Repeating Characters 解题报告

Posted 2020-08-29 notesbuddy

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.

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tag : two pointers     HashSet

思路：

（1）从第一个字符开始遍历，计算以每个字符开始的最长无重复子字符串。 

（2）每一计算的子串存在零时的HashSet里面。 注意HashSet这个数据结构， 增加元素是add()不是put().

 

public class Solution {
    public int lengthOfLongestSubstring(String s) {
        if(s == null || s.length() == 0) {
            return 0;
        }
        int max = 0;
        
        for(int i = 0; i < s.length(); i++) {
            HashSet<Character> set = new HashSet<Character>();
            set.add(s.charAt(i));
            if(max >= s.length() - i) {
                    break;
                }
            
            for(int j = i + 1; j < s.length(); j++) {
                
                if(set.contains(s.charAt(j))) {
                    break;
                } else {
                    set.add(s.charAt(j));
                }
            }
            max = Math.max(max, set.size());
        }
        
        return max;
       
    }
}