leetcode3

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.

class Solution {
   public int lengthOfLongestSubstring(String s) {
    int n=s.length();   //获取字符串长度
    int ans=0;          //最大值设为MAX 并且不断变化
    for(int i=0;i<n;i++)   //两层for循环遍历
    for(int j=i+1;j<=n;j++)
    {
    if(all(s,i,j)) ans=Math.max(ans, j-i);//遍历字符串的每一个子串，不断更新最大值
    }
    return ans;
   }
   public boolean all(String s,int start,int end)//判断是否相同使用Set集合
   {
    Set<Character> set=new HashSet<>();
    for(int i=start;i<end;i++)//for循环遍历字符串
    {
    Character c=s.charAt(i);//使用charAt遍历字符串中的每一个位置
    if(set.contains(c))return false;//假如存在，返回false    +0
    set.add(c);若不存在，则为true    +1
    }
    return true;
   }
}