leetcode刷题之旅（3）Longest Substring Without Repeating Characters

题目描述

Given a string, find the length of the longest substring without repeating characters.

样例

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 subsequenceand not a substring.

思路分析

求最长子字符串的长度，方法一是自己写的，很奇怪，O（n2）就已经超时了，，n，方法二是看讨论区的，hashmap解法，O（n）

基本思路：遍历字符串，遇到相同字符即停止，统计长度，大于max则赋值

代码

方法一

 public int lengthOfLongestSubstring(String s)
	 {
		 StringBuffer str = new StringBuffer();
		 int max = 0;
		 for (int i=0; i<s.length(); i++)
		 {
			 for (int j=i; j<s.length(); i++)
			 {
				 if (!str.toString().contains("s.charAt(j)"))
				 {
					 str.append(s.charAt(j));
				 }
				 else 
				 {
					 max = Math.max(max, str.length());
				 }
			 }
		 }
	     return max; 
	 }

方法二

 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;
    }