[Solved] Count Asterisks LeetCode Contest Problem

Count Asterisks: You are given a string s, where every two consecutive vertical bars '|' are grouped into a pair. In other words, the 1^st and 2^nd '|' make a pair, the 3^rd and 4^th '|' make a pair, and so forth.

Return the number of '*' in s, excluding the '*' between each pair of '|'.

Note that each '|' will belong to exactly one pair.

Example 1:

Input: s = "l|*e*et|c**o|*de|"
Output: 2
Explanation: The considered characters are underlined: "l|*e*et|c**o|*de|".
The characters between the first and second '|' are excluded from the answer.
Also, the characters between the third and fourth '|' are excluded from the answer.
There are 2 asterisks considered. Therefore, we return 2.

Example 2:

Input: s = "iamprogrammer"
Output: 0
Explanation: In this example, there are no asterisks in s. Therefore, we return 0.

Example 3:

Input: s = "yo|uar|e**|b|e***au|tifu|l"
Output: 5
Explanation: The considered characters are underlined: "yo|uar|e**|b|e***au|tifu|l". There are 5 asterisks considered. Therefore, we return 5.

Constraints:

• 1 <= s.length <= 1000
• s consists of lowercase English letters, vertical bars '|', and asterisks '*'.
• s contains an even number of vertical bars '|'.

Solution

Explanation

Parse the input, if currently met odd bars, we count *.

Complexity

Time O(n)
Space O(1)

Java

    public int countAsterisks(String s) {
        int res = 0, bars = 0;
        for (int i = 0; i < s.length(); ++i) {
            if (s.charAt(i) == '*' && bars % 2 == 0)
                res++;
            if (s.charAt(i) == '|')
                bars++;
        }
        return res;
    }

C++

    int countAsterisks(string s) {
        int res = 0, sign = 1;
        for (char& c : s)
            if ((sign ^= c == '|') && c == '*')
                res++;
        return res;
    }

Python
Space O(n)

    def countAsterisks(self, s: str) -> int:
        return sum([a.count('*') for a in s.split('|')][0::2])

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