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.

思路：对于没个i,我们向前探索一直到s.charAt(i)==s.charAt(j),i-j就是dp[i]的值，此时j最小循环到的值是j

代码如下(已通过leetcode)

public class Solution {
   public int lengthOfLongestSubstring(String s) {
    if(s.length()==0) return 0;
    if(s.length()==1) return 1;
      int dp[]=new int[s.length()];
      int i,j;
      int maxlen=0;
      boolean flag=false;
      dp[0]=1;
      int start=0;
      for(i=1;i<s.length();i++) {
      for(j=i-1;j>=start;j--) {
      if(s.charAt(i)==s.charAt(j)) {
      flag=true;
      start=j;
      dp[i]=i-j;
      break;
      }
      }
      if(!flag) {
      dp[i]=dp[i-1]+1;
      }
      if(dp[i]>maxlen) {
      maxlen=dp[i];
      }
      flag=false;
      }
     return maxlen;  
   }
}