leetcode：Longest Substring Without Repeating Characters

求出串S最长的不重复子串

定义数组ans[] , ans[i]表示以第i个字符结尾的最长不重复子串的长度为ans[i]，

那么可知：

ans[i] = ans[i - 1] + 1,如果第i个字符在S(i - 1 - ans[i - 1])......S(i -1)的范围内没有出现过

否则 ans[i] = i - 最后一次出现的位置;

public class Solution {
public int lengthOfLongestSubstring(String s) {
if (s.length() == 0) {
return 0;
}
HashMap<Character, Integer> map = new HashMap<>();
int[] ans = new int[s.length()];
ans[0] = 1;
map.put(s.charAt(0), 0);
int max = 1;
for (int i = 1, len = s.length(); i < len; ++i) {
Integer site = map.get(s.charAt(i));
if (site == null || site < i - ans[i - 1]) {
ans[i] = ans[i - 1] + 1;
} else {
ans[i] = i - site;
}
map.put(s.charAt(i), i);
if (ans[i] > max) {
max = ans[i];
}
}
// for (int k : ans) {
// System.out.print(k + " ");
// }
return max;
}
}