leetcode 3. 无重复字符的最长子串——滑动窗口

题目

leetcode 3. 无重复字符的最长子串

解法一：HashMap 去重

class Solution {
    public int lengthOfLongestSubstring(String s) {
        // 滑动窗口
        int len = s.length();
        int max = 0;
        int left = 0;
        HashMap<Character, Integer> map = new HashMap<>();
        for (int i = 0; i < len; i++){
            if(map.containsKey(s.charAt(i))){
                left = Math.max(left, map.get(s.charAt(i)) + 1);
            }
            map.put(s.charAt(i), i);
            max = Math.max(max, i-left+1);
        }
        return max;

    }
}

• 时间复杂度：O(n)
• 空间复杂度：O(n)

解法二：滑动窗口

class Solution {
    public int lengthOfLongestSubstring(String s) {
        // 滑动窗口
        int len = s.length();
        int max = 0;
        int left = 0, right = 0, start = 0;
        Map<Character, Integer> window = new HashMap<>();

        while (right < len) {
            char c = s.charAt(right);
            right++;
            window.put(c, window.getOrDefault(c, 0) + 1);
            while (window.get(c) > 1) {
                char d = s.charAt(left);
                left++;
                window.put(d, window.get(d)-1);
            }
            max = Math.max(max, right - left);
        }
        return max;
    }
}

• 时间复杂度：O(n)
• 空间复杂度：O(n)