3 Longest Substring Without Repeating Characters

3. Longest Substring Without Repeating Characters

1. Question

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.

2. Implementation

(1) Two Pointer + Hash

class Solution {
    public int lengthOfLongestSubstring(String s) {
        if (s == null || s.length() == 0) {
            return 0;
        }

        int maxLen = 0;
        int start = 0, end = 0;
        int count = 0;
        int[] map = new int[256];

        while (end < s.length()) {
            if (map[s.charAt(end)] > 0) {
                ++count;
            }
            ++map[s.charAt(end)];
            ++end;

            while (count > 0) {
                if (map[s.charAt(start)] > 1) {
                    --count;
                }
                --map[s.charAt(start)];
                ++start;
            }
            maxLen = Math.max(maxLen, end - start);
        }
        return maxLen;
    }
}

3. Time & Space Complexity

Two Pointer + Hash: 时间复杂度O(n), 空间复杂度O(1)