[LeetCode]3.Longest Substring Without Repeating Characters

Given a string, find the length of the longest substring without
repeating characters.

Example 1:

Input: "abcabcbb" Output: 3 Explanation: The answer is "abc", with
the length of 3. Example 2:

Input: "bbbbb" Output: 1 Explanation: The answer is "b", with the
length of 1. Example 3:

Input: "pwwkew" Output: 3 Explanation: 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.

对xxx串，它的最长不重复子串情况可以完全由xx可以决定，确认是dp问题
确定状态转移方程，定义dp[i]为与当前串构成不重复串的index
dp[i]=Math.max(dp[i-1],count[s.charAt(i-1)]+1);

public int lengthOfLongestSubstring(String s) {
    int ret=0;
    int l=s.length();
    int[] dp=new int[l+1];
    int[] count=new int[128];
    for(int i=1;i<=l;i++){
        dp[i]=Math.max(dp[i-1],count[s.charAt(i-1)]+1);
        ret=Math.max(ret,i+1-dp[i]);
        count[s.charAt(i-1)]=i;
    }  
    return ret; 
}