leetcode——Longest Substring Without Repeating Characters

原題：

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.

解析：要求尋找字符串中的無重複字符的最長子串長度。顯然，最長子串的長度也不會超過256，所以可以記錄字串中各字符出現次數，保證子串中每個字符出現次數爲1即可，算法複雜度爲O(n)。

class Solution {
public:
	int lengthOfLongestSubstring(string s) {
		if(s.length()<=1)	return s.length();
		int a[256] = {0};
		int j=0, k=1, l=s.length(), max=1;
		a[s[0]] = 1;
		while(k<l && (l-j)>max))
		{
			if(a[s[k]]==0)
			{
				a[s[k++]] = 1;
				if(k-j > max)	max = k-j;
			}
			else	a[s[j++]] = 0;
		}
		return max;
	}
};