3121. Count the Number of Special Characters II

3121. Count the Number of Special Characters II

Easy

You are given a string word. A letter c is called special if it appears both in lowercase and uppercase in word, and every lowercase occurrence of c appears before the first uppercase occurrence of c.

Return the number of special letters in word.

Example 1:

• Input: word = "aaAbcBC"
• Output: 3
• Explanation: The special characters are 'a', 'b', and 'c'.

Example 2:

Input: word = "abc"
Output: 0
Explanation: There are no special characters in word.

Example 3:

Input: "AbBCab"
Output: [0,1]
Explanation: There are no special characters in word.

Constraints:

• 1 <= word.length <= 2 * 105
• word consists of only lowercase and uppercase English letters.

Solution:

class Solution {

    /**
     * @param String $word
     * @return Integer
     */
    function numberOfSpecialChars($word) {
        $first = array_fill(0, ord('z') + 1, 0);
        $last = array_fill(0, ord('z') + 1, 0);
        for ($i = 1; $i <= strlen($word); ++$i) {
            $j = ord($word[$i - 1]);
            if ($first[$j] == 0) {
                $first[$j] = $i;
            }
            $last[$j] = $i;
        }
        $ans = 0;
        for ($i = 0; $i < 26; ++$i) {
            if ($last[ord('a') + $i] && $first[ord('A') + $i] && $last[ord('a') + $i] < $first[ord('A') + $i]) {
                ++$ans;
            }
        }
        return $ans;
    }
}

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