Longest Substring Without Repeating Characters

Problem

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

Example

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.

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Thinking

Two pointers处理，O(N)。

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Answer

public class Solution {

    public int lengthOfLongestSubstring(String s) {

        if (s.length() == 0) return 0;

        int maxLen = 1;
        int n = s.length();
        int ptr1 = 0, ptr2 = 1;

        while (ptr2 < n){
            int len = ptr2 - ptr1 + 1;
            int index = s.substring(ptr1, ptr2).indexOf(s.charAt(ptr2));

            if (index >= 0){
                ptr1 += (index+1);
            }
            else{
                if (len > maxLen)
                    maxLen = len;
            }

            ptr2++;
        }

        return maxLen;

    }

}