(leetcode)3.一个数组的最长子列Longest Substring Without Repeating Characters--Java

Longest Substring Without Repeating Characters

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.

找到最长的子字符串，其思想是一次遍历，两个指针i和j，存在map中，如果没有重复的，则直接+1，如果有重复的，则把j的位置后移，然后计算max

public int lengthOfLongestSubstring(String s)

{if(s.length()==0)return0;

HashMap<Character, Integer>map=newHashMap<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);  //关键点：j只能往后走，不能往前看。

}

map.put(s.charAt(i),i);

max= Math.max(max,i-j+1);

}

return max;

}