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.
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用HashMap
public int lengthOfLongestSubstring(String s) { if (s.length()==0) return 0; HashMap<Character, Integer> map = new HashMap<Character, Integer>(); int max=0; for (int i=0, j=0; i<s.length(); ++i){ if (map.containsKey(s.charAt(i))){ j = Math.max(j,map.get(s.charAt(i))+1); } map.put(s.charAt(i),i); max = Math.max(max,i-j+1); } return max; }
用Set
核心算法和上面的很类似,把出现过的字符都放入set中,遇到set中没有的字符就加入set中并更新结果res,如果遇到重复的,则从左边开始删字符,直到删到重复的字符停止
public int lengthOfLongestSubstring(String s) { Set set=new HashSet(); int j=0,i=0,max=0; while(i<s.length()){ if(!set.contains(s.charAt(i))){ set.add(s.charAt(i)); i++; // System.out.println(set); max=Math.max(max,set.size()); //System.out.println(max); }else{ set.remove(s.charAt(j)); j++; } } return max; }
还有一种很巧妙地方法 复杂度只有O(n)
建立一个256位大小的整型数组来代替哈希表,这样做的原因是ASCII表共能表示256个字符,所以可以记录所有字符,然后我们需要定义两个变量res和left,其中res用来记录最长无重复子串的长度,left指向该无重复子串左边的起始位置,然后我们遍历整个字符串,对于每一个遍历到的字符,如果哈希表中该字符串对应的值为0,说明没有遇到过该字符,则此时计算最长无重复子串,i - left +1,其中i是最长无重复子串最右边的位置,left是最左边的位置,还有一种情况也需要计算最长无重复子串,就是当哈希表中的值小于left,这是由于此时出现过重复的字符,left的位置更新了,如果又遇到了新的字符,就要重新计算最长无重复子串。最后每次都要在哈希表中将当前字符对应的值赋值为i+1
public int lengthOfLongestSubstring(String s) { int[] m = new int[256]; Arrays.fill(m, -1); int res = 0, left = -1; for (int i = 0; i < s.length(); ++i) { left = Math.max(left, m[s.charAt(i)]); m[s.charAt(i)] = i; res = Math.max(res, i - left); } return res; }
- Longest Substring Without Repeating Characters
- Longest Substring Without Repeating Characters
- Longest Substring Without Repeating Characters
- Longest Substring Without Repeating Characters
- Longest Substring Without Repeating Characters
- Longest Substring Without Repeating Characters
- Longest Substring Without Repeating Characters
- Longest Substring Without Repeating Characters
- Longest Substring Without Repeating Characters
- Longest Substring Without Repeating Characters
- Longest Substring Without Repeating Characters
- Longest Substring Without Repeating Characters
- Longest Substring Without Repeating Characters
- Longest Substring Without Repeating Characters
- Longest Substring Without Repeating Characters
- Longest Substring Without Repeating Characters
- Longest Substring Without Repeating Characters
- Longest Substring Without Repeating Characters
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