LeetCode 3. Longest Substring Without Repeating Characters

leetCode 3. Longest Substring Without Repeating Characters

Description

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.

    class Solution {
        public int lengthOfLongestSubstring(String s) {
            int n = s.length();
            Set<Character> set = new HashSet<>();
            int ans = 0, i = 0, j = 0;
            while (i < n && j < n) {
                if (!set.contains(s.charAt(j))) {
                    set.add(s.charAt(j++));
                    ans = Math.max(ans, j - i);
                }
                else {
                    set.remove(s.charAt(i++));
                }
            }
            return ans;
        }
    }

    public class Solution {
    public int lengthOfLongestSubstring(String s) {
        int n = s.length(), ans = 0;
        int[] index = new int[128]; // current index of character
        // try to extend the range [i, j]
        for (int j = 0, i = 0; j < n; j++) {
            i = Math.max(index[s.charAt(j)], i);
            ans = Math.max(ans, j - i + 1);
            index[s.charAt(j)] = j + 1;
        }
        return ans;
    }
}