Leetcode.寻找不重复的最长子字符串

题号：3

原题：Longest Substring Without Repeating CharactersGiven a string, find the length of the longest substring without repeating characters.

// 给定一个字符串，找到最长子串，里面不能有重复的字符。

Examples:Given "abcabcbb", the answer is "abc", which the length is 3. //字长子字符创可能出现在前面，也可能出现在后面。

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. // 子字符串必需连续

Subscribe to see which companies asked this question.

设计：

举例：“abcdbef”，找到两个子序列，一个head表示一个子序列，第二个子序列更长些，max=max2=5。

一个超时的方法：

public int lengthOfLongestSubstring(String s) {
    	HashMap map = new HashMap();
    	char[] cs = s.toCharArray();
    	
    	int max = 0;
    	int order = 0;
    	int head = 0;
    	for(char i:cs) {
    		if( map.containsKey(i)) {
    			max = Math.max(order-head, max);
    			head = Math.max(map.get(i)+1, head);
    		}
    		map.put(i, order);
    		order++;
    	}
    	max = Math.max(order-head, max);
        return max;
    }

成功方法：

public class Solution {
    public int lengthOfLongestSubstring(String s) {
    	HashMap map = new HashMap();
    	
    	int max = 0;
    	int order = 0;
    	int head = 0;
    	for(int i = 0; i < s.length(); i++) {
    		 if (map.containsKey(s.charAt(i))) { // 字符串单独转换
    			max = Math.max(order-head, max);
    			head = Math.max(map.get(s.charAt(i))+1, head);
    		}
    		map.put(s.charAt(i), order);
    		order++;
    	}
    	
    	max = Math.max(order-head, max);
        return max;
    }
}