LeetCode 3. Longest Substring Without Repeating Characters
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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:1.将每组子串的字母存在hashset中,判断当前字母是否存在set中(hash查找效率高)。
2.若存在则判断下一组子串。下组子串的初始位置在重复字母处位置+1。
3.若不存在则将此字母存在容器中,并判断当然容器大小是不是最大, 若是最大表示当前长度最大。
如abcabcbb,
1.容器中一次存入第一个子串abc,到第2个a事与第一个a重复,容器中移除第一个a到第一个子串的初始位置0的所有元素,容器中的元素为abc。
2.容器中子串bca,第二个b重复,相同办法。
注:判断下个子串的初始位置,为重复字母的位置+1,类似于kmp算法。
1 public int lengthOfLongestSubstring(String s) { 2 int max = 0; 3 int flag = 0; 4 Set<Character> set = new HashSet<Character>(); 5 char[] a = s.toCharArray(); 6 for(int i=0;i<a.length;i++) { 7 if(!set.contains(a[i])) { 8 set.add(a[i]); 9 if(max<set.size()) { 10 max = set.size(); 11 } 12 }else { 13 int j = flag; 14 while(a[i]!=a[j]) { 15 set.remove(a[j]); 16 j++; 17 } 18 flag = j+1; 19 } 20 //System.out.println(set.toString()); 21 } 22 return max; 23 24 }
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