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.

package November;public class LongestSubstringWithoutRepeatingCharacters {public static int lengthOfLongestSubstring(String s) {if(s==null||s.isEmpty())return 0;int max = 1;int index = 1;int sum = 1;while (index < s.length()) {int pos=existInSubstring(s,index-sum,index-1,s.charAt(index));if (pos==-1) {sum++;if(sum>max){//这里需要注意，及时更新max值max=sum;}index++;} else {if (sum > max) {max = sum;}sum = 1;index=pos+2;//这里需要注意，回退点不是index+1，而是上一个重复的地方，例如dvdf，应该是3，而不是2}}return max;}public static int existInSubstring(String s, int start, int end,char c) {for (int index = start; index <= end; index++) {if (s.charAt(index) == c)return index;}return -1;}public static void main(String[] args) {//String s1 = "abcabcbb";//String s2 = "bbbbb";//String s3 = "pwwkew";String s4="au";String s5="dvdf";//System.out.println(lengthOfLongestSubstring(s1));//System.out.println(lengthOfLongestSubstring(s2));//System.out.println(lengthOfLongestSubstring(s3));System.out.println(lengthOfLongestSubstring(s4));System.out.println(lengthOfLongestSubstring(s5));}}