g0001_0100.s0003_longest_substring_without_repeating_characters.Solution Maven / Gradle / Ivy

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Java-based LeetCode algorithm problem solutions, regularly updated

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package g0001_0100.s0003_longest_substring_without_repeating_characters;

// #Medium #Top_100_Liked_Questions #Top_Interview_Questions #String #Hash_Table #Sliding_Window
// #Algorithm_I_Day_6_Sliding_Window #Level_2_Day_14_Sliding_Window/Two_Pointer #Udemy_Strings
// #Big_O_Time_O(n)_Space_O(1) #2023_08_09_Time_2_ms_(99.88%)_Space_43.7_MB_(58.61%)

/**
 * 3 - Longest Substring Without Repeating Characters\.
 *
 * Medium
 *
 * Given a string `s`, find the length of the **longest substring** without repeating characters.
 *
 * **Example 1:**
 *
 * **Input:** s = "abcabcbb"
 *
 * **Output:** 3
 *
 * **Explanation:** The answer is "abc", with the length of 3. 
 *
 * **Example 2:**
 *
 * **Input:** s = "bbbbb"
 *
 * **Output:** 1
 *
 * **Explanation:** The answer is "b", with the length of 1. 
 *
 * **Example 3:**
 *
 * **Input:** s = "pwwkew"
 *
 * **Output:** 3
 *
 * **Explanation:** The answer is "wke", with the length of 3. Notice that the answer must be a substring, "pwke" is a subsequence and not a substring. 
 *
 * **Example 4:**
 *
 * **Input:** s = ""
 *
 * **Output:** 0 
 *
 * **Constraints:**
 *
 * *   0 <= s.length <= 5 * 10⁴
 * *   `s` consists of English letters, digits, symbols and spaces.
**/
public class Solution {
    public int lengthOfLongestSubstring(String s) {
        int[] lastIndices = new int[256];
        for (int i = 0; i < 256; i++) {
            lastIndices[i] = -1;
        }
        int maxLen = 0;
        int curLen = 0;
        int start = 0;
        for (int i = 0; i < s.length(); i++) {
            char cur = s.charAt(i);
            if (lastIndices[cur] < start) {
                lastIndices[cur] = i;
                curLen++;
            } else {
                int lastIndex = lastIndices[cur];
                start = lastIndex + 1;
                curLen = i - start + 1;
                lastIndices[cur] = i;
            }
            if (curLen > maxLen) {
                maxLen = curLen;
            }
        }
        return maxLen;
    }
}