Longest Substring Without Repeating Charactersdf

首先呢 可能会想到用一个windows去放这些东西.

可能会想到hashtable去. 但是hashtable 无法用Index去查询.

abcabcbb. hashtable: abc 当第二个a来的时候, 我们想bca 貌似不好实现.

这种情况就很像LRU. 用 node<prev,next>连接，用hashtable<key,node>去记录位置.

这就很麻烦了,有没有别的选择呢？

字符反而比integer的这种类型题要简单，因为最多就256种可能性. 可以看成有限制的integer类型题.所以不要心存恐惧啦.

you would need two indices to record the head and the tail of the current substring. 两个index完美的window.

Ok.所以我们需要two index完成window. c[256]记录location.

public class Solution {
public int lengthOfLongestSubstring(String s) {
// Start typing your Java solution below
// DO NOT write main() function
int length = s.length();
if (length == 0) {
return 0;
}
int [] countTable = new int[256];
Arrays.fill(countTable, -1);
int max = 1;
int start = 0;
int end = 1;

countTable[s.charAt(0)] = 0;
while (end < length) {
//Has not reached a duplicate char
if (countTable[s.charAt(end)] >= start) {
start = countTable[s.charAt(end)] + 1;
}
max = Math.max(max, end - start + 1);
countTable[s.charAt(end)] = end;
end++;
}
return max;
}
}