找到没有重复字符的最长子串 - Java

Question

我试图解决一个 leetcode 问题，但我的解决方案没有为其中一个测试用例返回正确的值。我想为这个解决方案实现两指针技术（如果我使用的技术有误，欢迎提出建议来解释正确的方法）。详情如下：

Leetcode 题目：

Longest Substring Without Repeating Characters.

问题：

Given a string, find the length of the longest substring without repeating characters. ( return int )

我的解决方案：

    public int lengthOfLongestSubstring(String s) {
        //place holder for me to create a "sub-string"
        String sub = "";
        
        //counter variable to count the characters in the substring
        int count = 0;
        int maxCount = 0;
        
        //my attempt at a TWO POINTER TECHNIQUE
        //pointers - to determine when the loop should break
        int head = 0;
        int tail = s.length();
        
        //this variable was intended to be used with the "indexOf" method, as the "start from" index...
        int index = 0;
        
        while(head < tail){
            //check if the next character in the string was already added to my substring.
            int val = sub.indexOf(s.charAt(head), index);
            
            //we proceed if it is -1 because this means the substring didnt previously contain that character
            if(val == -1){
                //added character to my substring
                sub+= s.charAt(head);
                count++;
                head++;
            } else {
                //reset data to default conditions, while continuing at the "head index" and check the rest of the substring
                count = 0;
                sub =  "";
            }
            //determine what the length of the longest substring.
            maxCount = count > maxCount ? count : maxCount;
        }
        return maxCount;
    }

我通过了测试用例：

> "" = expect 0
> " " = expect 1
> "abcabcbb" = expect 3
> "bbbbb" = expect 1
> "pwwkew" = expect 3
> "aab" = expect 2

我失败的测试用例：

> "dvdgd" = expect 3, but got 2
> "dvjgdeds" = expect 5, but got 4
> "ddvbgdaeds" = expect 6, but got 4

可能的问题：

I believe the issue occurred because it moves pass the index with "v", and then processes the substring "dg". So I attempted to change the solution, but fixing that issue caused all my other cases to return errors so I figured that attempt at a fix should be tossed out.

我也尝试过：

I also attempted to manipulate the "indexOf" method to change the start index, whenever the character was found in the string. This however generated an infinite loop.

我已经尝试解决这个问题几个小时了，我被踩住了。因此，我们将不胜感激任何帮助。如果可以的话，请详细说明，我是 DSA 和编程的新手，非常感谢。如果需要我提供更多信息，请告诉我我会尽力回答。

Answer 1

好了，给你：

public static int lengthOfLongestSubstring(String s) {
    //place holder for me to create a "sub-string"
    String sub = "";
    
    //counter variable to count the characters in the substring
    int count = 0;
    int maxCount = 0;
    
    //my attempt at a TWO POINTER TECHNIQUE
    //pointers - to determine when the loop should break
    int head = 0;
    int tail = s.length();
    
    //this variable shows where to start from 
    int index = 0;
    
    while(head < tail){
        //check if the next character in the string was already added to my substring.
        int val = sub.indexOf(s.charAt(head)); //search whole substing
        
        //we proceed if it is -1 because this means the substring didnt previously contain that character
        if(val == -1){
            //added character to my substring
            sub+= s.charAt(head);
            count++;
            head++;
            //determine what the length of the longest substring.
            maxCount = count > maxCount ? count : maxCount;
            System.out.println(sub); //let's see what we got so far
        } else {
            //reset data to default conditions, while continuing at the "head index" and check the rest of the substring
            count = 0;
            sub =  "";
            head=index+1; //begin from the next letter 
            index++; //move
        }
        
        
    }
    return maxCount;
}

找到没有重复字符的最长子串 - Java

Find the Longest Substring without Repeating Characters - Java

java

string

substring

string-length