2678. Number of Senior Citizens

Problem

You are given a 0-indexed array of strings details. Each element of details provides information about a given passenger compressed into a string of length 15. The system is such that:

• The first ten characters consist of the phone number of passengers.
• The next character denotes the gender of the person.
• The following two characters are used to indicate the age of the person.
• The last two characters determine the seat allotted to that person.

Return **the number of passengers who are **strictly **more than 60 years old.**

Example 1:

Input: details = ["7868190130M7522","5303914400F9211","9273338290F4010"]
Output: 2
Explanation: The passengers at indices 0, 1, and 2 have ages 75, 92, and 40. Thus, there are 2 people who are over 60 years old.

Example 2:

Input: details = ["1313579440F2036","2921522980M5644"]
Output: 0
Explanation: None of the passengers are older than 60.

Constraints:

• 1 <= details.length <= 100
• details[i].length == 15
• details[i] consists of digits from '0' to '9'.
• details[i][10] is either 'M' or 'F' or 'O'.
• The phone numbers and seat numbers of the passengers are distinct.

Solution (Java)

class Solution {
    public int countSeniors(String[] s) {
        int ans=0;
        for(String ss:s){
            int a1=ss.charAt(11)-'0';
            int a2=ss.charAt(12)-'0';
            if((a1*10)+a2>60)
                ans++;
        }
        return ans;
    }
}

Explain:

nope.

Complexity:

• Time complexity : O(n).
• Space complexity : O(n).