003_LeetCode_3 Longest Substring Without Repeating Characters 题解

Descripton

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Given a string, find the length of the longest substring without repeating characters.

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Examples:

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• 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.

返回一个字符串中，不包含重复元素的连续子序列的长度。

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解：

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使用HashMap，以字符串对应的元素作为key，下标作为value。遍历字符串，判断当前元素是否已经存在于哈希表中：

• 若存在则，删除上次存入的下标以及该下标之前的元素；将当前元素存入哈希表，更新起始的遍历位置和子串长度。

• 若不存在，则将当前元素存入哈希表,子串长度加一，并于最大子串长度比较。

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java代码：

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class Solution {    public int lengthOfLongestSubstring(String s) {        if (s == null) return 0;        HashMap<Character, Integer> map =  new HashMap<Character, Integer>();        int start = 0, maxLen = 0, subLen = 0;        for (int i = 0; i < s.length(); i++) {            if (!map.containsKey(s.charAt(i))){                map.put(s.charAt(i), i);                subLen++;                if (subLen > maxLen) maxLen = subLen;            }else {                int index = map.get(s.charAt(i));                for (int j = start; j <= index; j++) {                    map.remove(s.charAt(j));                }                map.put(s.charAt(i), i);                start = index + 1;                subLen = i - index;            }        }        return maxLen;    }}