Leetcode 3 Longest Substring Without Repeating Characters

最新推荐文章于 2025-05-18 01:04:12 发布

原创最新推荐文章于 2025-05-18 01:04:12 发布 · 212 阅读

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本文探讨了如何寻找字符串中最长的无重复字符子串，提供了两种高效算法实现，利用哈希表跟踪字符位置，避免了重复计算，实现O(n)时间复杂度。

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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.

想了很久没想出来，借鉴了一点题解：

本题类似于最长公共子序列的问题，动规的思想

class Solution {
    public int lengthOfLongestSubstring(String s) {
        int n = s.length(), ans = 0;
        Map<Character,Integer> map = new HashMap<>();
        for(int i = 0 ,j = 0;j < n ;j++){
            if(map.containsKey(s.charAt(j))){
                i = Math.max(map.get(s.charAt(j)),i);
            }
            ans = Math.max(ans,j - i + 1);
            map.put(s.charAt(j),j+1);
        }
        return ans;
    }
}

另一个解：

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;
    }
}