feat: solve No.2678

Author: BaffinLee

2601-2700/2678. Number of Senior Citizens.md

@@ -0,0 +1,83 @@
+# 2678. Number of Senior Citizens
+
+- Difficulty: Easy.
+- Related Topics: Array, String.
+- Similar Questions: .
+
+## 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
+
+```javascript
+/**
+ * @param {string[]} details
+ * @return {number}
+ */
+var countSeniors = function(details) {
+    var count = 0;
+    for (var i = 0; i < details.length; i++) {
+        if (details[i][11] > '6' || (details[i][11] === '6' && details[i][12] > '0')) {
+            count += 1;
+        }
+    }
+    return count;
+};
+```
+
+**Explain:**
+
+nope.
+
+**Complexity:**
+
+* Time complexity : O(n).
+* Space complexity : O(1).