3.longest-substring-without-repeating-characters

Description:

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

Constraints:

• 0 <= s.length <= $5*10^4$
• s consists of English letters, digits, symbols and spaces

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Sliding Window

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Appropriate Answer (Sliding Window):

<?php

namespace LeetCode\LongestSubstringWithoutRepeatintCharacters;

class Solution
{

    /**
     * @param string $string
     * @return int
     */
    public function lengthOfLongestSubstring($string)
    {
        $answer = 0;

        $length = strlen($string);
        if ($length == 0) {
            return $answer;
        }

        $windowLeft = 0;
        $windowRight = 0;
        $usedCharacters = [];
        while ($windowRight < $length) {
            $character = $string[$windowRight];

            while (
                isset($usedCharacters[$character]) &&
                $windowLeft <= $usedCharacters[$character]
            ) {
                $windowLeft++;
            }

            $usedCharacters[$character] = $windowRight;
            $windowRight++;

            $answer = max($answer, $windowRight - $windowLeft);
        }

        return $answer;
    }
}

• Time Complexity: $O(n)$

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ʕ •ᴥ•ʔ：一開始有嘗試暴力解，但最後一個test case跑不過。