leetcode 3. Longest Substring Without Repeating Characters

最新推荐文章于 2021-12-03 15:58:56 发布

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最新推荐文章于 2021-12-03 15:58:56 发布

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分类专栏： LeetCode 文章标签： java leetcode

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本文介绍了解决字符串中寻找最长无重复字符子串问题的两种方法。通过使用哈希表或字符计数数组，有效地追踪当前扫描范围内字符的状态，从而实现高效查找。这种方法适用于编程面试和技术挑战。

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题目

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.

解析

方法一

class Solution {
    public int lengthOfLongestSubstring(String s) {
        int n = s.length();
        if (n == 0) return 0;
        int max = 0;
        Map<Character, Integer> map = new HashMap<>();
        for (int i = 0, j = 0; i < n; i++) {
            if (map.containsKey(s.charAt(i))) {
                // + 1是因为重复，向后移动一位
                j = Math.max(j, map.get(s.charAt(i)) + 1);
            }
            map.put(s.charAt(i), i);
            max = Math.max(max, i - j + 1);
        }
        return max;
    }
}

方法二

class Solution {
    public int lengthOfLongestSubstring(String s) {
        int[] map = new int[128];
        int count = 0, begin = 0, end = 0, d =0;
        while (end < s.length()) {
            if (map[s.charAt(end++)]++ > 0) count++;//重复
            while (count > 0) if (map[s.charAt(begin++)]-- > 1) count--;
            d = Math.max(d, end - begin);
        }
        return d;
    }
}