LeetCode 3. Longest Substring Without Repeating Characters（最长不重复子串）

原题网址：https://leetcode.com/problems/longest-substring-without-repeating-characters/

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.
方法：通过哈希表/直方图来标记字符是否出现过。

public class Solution {
public int lengthOfLongestSubstring(String s) {
if (s == null) return 0;
boolean[] has = new boolean[256];
int max = 0;
int from = 0;
char[] sa = s.toCharArray();
for(int i=0; i<sa.length; i++) {
while (has[sa[i]]) has[sa[from++]] = false;
has[sa[i]] = true;
max = Math.max(max, i-from+1);
}
return max;
}
}