3、Longest Substring Without Repeating Characters，longestrepeating

3、Longest Substring Without Repeating Characters，longestrepeating

Longest Substring Without Repeating Characters

Given a string, find the length of the longest substring without repeating characters. For example, the longest substring without repeating letters for “abcabcbb” is “abc”, which the length is 3. For “bbbbb” the longest substring is “b”, with the length of 1.

思路

使用Hash Table 定义两个参数i、j 其中i用来表示Hash表的key 而j用来进行计算max 使用了
map.get() map.put() map.containsKey() Math.max() 等

代码

public class Solution {
    public int lengthOfLongestSubstring(String s) {
          if (s.length()==0) return 0;
        HashMap<Character, Integer> map = new HashMap<Character, Integer>();  //创建一个map的实例对象
        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);  //如果字符串中有重复的字符则更新j的值
            } 
            map.put(s.charAt(i), i);
            max = Math.max(max,i-j+1);  //求出最大序列值
        }
        return max;
    }
}