【Leetcode】3. Longest Substring Without Repeating Characters

1.英文題目

Given a string, find the length of the longest substring without repeating characters.

Example 1:

Input: "abcabcbb"
Output: 3 
Explanation: The answer is , with the length of 3."abc"

Example 2:

Input: "bbbbb"
Output: 1
Explanation: The answer is , with the length of 1."b"

Example 3:

Input: "pwwkew"
Output: 3
Explanation: The answer is , with the length of 3. 
             Note that the answer must be a substring,  is a subsequence and not a substring."wke""pwke"

2.解題

package com.example.leetcode.medium;

public class LengthOfLongestSubstring {


    public static int lengthOfLongestSubstring(String s) {
        if (s == null||s.length()==0) {
            return 0;
        }
        int max = 1;
        int medium = 1;
        for (int i = 0, j = 1,k=1; k < s.length(); ) {
            String a = s.substring(i, j);
//            System.out.println(a);

            String b = s.substring(k, k+1);
//            System.out.println(b);
            if (a.contains(b)) {
                i++;
                j=i+1;
                k =i+1;
                medium=1;
            } else {
                j++;
                k++;
                medium++;
                if (medium > max) {
                    max = medium;
                }
            }

        }
        return max;
    }

    public static void main(String[] args) {
        System.out.println(lengthOfLongestSubstring("bbbb"));
    }
}

單元測試

package com.example.leetcode.medium;

import org.junit.Assert;
import org.junit.Test;

public class LengthOfLongestSubstringTest {


    @Test
    public void should_return_When_string_is_abcabcbb() {
        Assert.assertEquals(3, LengthOfLongestSubstring.lengthOfLongestSubstring("abcabcbb"));
    }



    @Test
    public void should_return_When_string_is_dvdf() {
        Assert.assertEquals(3, LengthOfLongestSubstring.lengthOfLongestSubstring("dvdf"));
    }

    @Test
    public void should_return_When_string_is_au() {
        Assert.assertEquals(2, LengthOfLongestSubstring.lengthOfLongestSubstring("au"));
    }

    @Test
    public void should_return_When_string_is_null_string() {
        Assert.assertEquals(0, LengthOfLongestSubstring.lengthOfLongestSubstring(""));
    }



    @Test
    public void should_return_When_string_is_bbbb() {
        Assert.assertEquals(1, LengthOfLongestSubstring.lengthOfLongestSubstring("bbbbb"));
    }


}