3. Longest Substring Without Repeating Characters

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.

Solution:

class Solution {

    /**
     * @param String $s
     * @return Integer
     */
    function lengthOfLongestSubstring($s) {
        $lastIndices = array_fill(0, 256, -1);
        $maxLen = 0;
        $curLen = 0;
        $start = 0;

        for ($i = 0; $i < strlen($s); $i++) {
            $cur = $s[$i];
            $curAscii = ord($cur);

            if ($lastIndices[$curAscii] < $start) {
                $lastIndices[$curAscii] = $i;
                $curLen++;
            } else {
                $lastIndex = $lastIndices[$curAscii];
                $start = $lastIndex + 1;
                $curLen = $i - $start + 1;
                $lastIndices[$curAscii] = $i;
            }

            if ($curLen > $maxLen) {
                $maxLen = $curLen;
            }
        }

        return $maxLen;
    }
}

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