3. 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.

public class Solution {
public int lengthOfLongestSubstring(String s) {
int[] last = new int[128];
int start = 0;
int len = 0;
char[] w = new char[s.length()];
w = s.toCharArray();
for(int i = 0; i < 128; i++)
last[i] = -1;//last数组用于保存新出现的字符的下标，一开始全部初始化为-1
for(int i = 0; i < s.length(); ++i){
if(last[w[i]-' '] >= start){ //当前这个字符出现过
if(i-start > len)
len = i-start;
start = last[w[i]-' '] + 1; //从这个字符首次出现的位置+1，重新扫描，相当于把前面抛开前面的字符串不谈
}
last[w[i]-' '] = i;//更新当前字符的下标
}
if(len > s.length() - start)//针对没有重复字符的字符串
return len;
else
return s.length() - start;
}
}