Longest Substring Without Repeating Characters

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• Difficulty: Medium

Description

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.

Thinking

• 返回字符串中的最长不重复子串的长度

Solution -1

• 32ms, beats 99.27%
• 自己的做法，有点暴力
• list 中存放不重复的子串，一旦当前字符 list 中存在，就不断的剔除子串的首个字符，直到剔除相同字符后

public static int lengthOfLongestSubstring(String s) {

    List<Character> list = new LinkedList<>();
    int result = 0;

    for (int i = 0; i < s.length(); i++) {

        char temp = s.charAt(i);
        if (list.contains(temp)) {

            while (list.contains(temp)) {
                list.remove(0);
            }

        }
        list.add(temp);
        result = Math.max(result, list.size());

    }

    return result;

}

Solution -2

• 22ms, beats 99.99%
• Leetcode 大神解法
• 滑动窗口思想：如果当前遇到的字符 j 同字符 i 相同，那么当前的不重复子串长度等于 length = j-i+1

public static int lengthOfLongestSubstring(String s) {

    int[] flag = new int[128];
    int result = 0;

    for (int i = 0, j = 0; j < s.length(); j++) {

        i = Math.max(flag[s.charAt(j)], i);
        result = Math.max(result, j-i+1);
        flag[s.charAt(j)] = j+1;

    }

    return result;

}