計數應用: 資深公民的數量 Number of Senior Citizens_Leetcode #2678

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題目敘述 Number of Senior Citizens

給定一個旅客的車票字串陣列，每個字串的最後第四個和第三個數字代表旅客的年齡。

例如: XXX...XXX2015 代表旅客年齡為20歲。

請計算總共有多少位乘客的年齡 > 60 歲?

測試範例

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.

約束條件

Constraints:

• 1 <= details.length <= 100

輸入陣列長度介於1~100之間。

• details[i].length == 15

每個旅客字串長度為15

• details[i] consists of digits from '0' to '9'.

旅客字串裡面的數字一定在0~9的範圍內

• details[i][10] is either 'M' or 'F' or 'O'.

第11碼代表性別

• The phone numbers and seat numbers of the passengers are distinct.

每位旅客的電話號碼和座號保證都相異

演算法 生成式 + 計數

根據題意，擷取年齡所在的字串位置，轉成數字，統計有多少位旅客 > 60歲。

Python生成式的教學請參考這篇文章

程式碼 生成式 + 計數

class Solution:

    def countSeniors(self, details: List[str]) -> int:
       

        return sum( ( 1  for d in details if int(d[-4:-2]) > 60 ) )

複雜度分析

時間複雜度:O(n)

線性掃描每一筆旅客資料，所需時間為O(n)

空間複雜度: O(1)

所用到的都是固定尺寸的臨時變數，所需空間為O(1)，常數級別。

Reference

[1] Number of Senior Citizens - LeetCode