How do I solve the 'Number of Senior Citizens' problem?

Extract the passenger's age from the 11th and 12th characters of each string, convert it to an integer, and count how many are over 60 years old.

What is the time complexity of the 'Number of Senior Citizens' problem?

The time complexity is O(n), where n is the number of passengers in the array.

Can I solve this problem without converting the age string to an integer?

No, you must convert the age substring to an integer to perform the comparison against 60.

What are common mistakes when solving the 'Number of Senior Citizens' problem?

Common mistakes include incorrect string indexing, failing to convert the age substring to an integer, and unnecessary overcomplication of the solution.

How can I handle edge cases in the 'Number of Senior Citizens' problem?

Make sure to account for edge cases like empty arrays or passengers exactly 60 years old by using the strict 'greater than' condition.

#2678

Easy

auto_awesome数组·string

LeetCode 题解工作台

老人的数目

给你一个下标从 0 开始的字符串数组 details 。 details 中每个元素都是一位乘客的信息，信息用长度为 15 的字符串表示，表示方式如下：前十个字符是乘客的手机号码。接下来的一个字符是乘客的性别。接下来两个字符是乘客的年龄。最后两个字符是乘客的座位号。请你返回乘客中年龄严格…

数组字符串

题目描述

给你一个下标从 0 开始的字符串数组 details 。details 中每个元素都是一位乘客的信息，信息用长度为 15 的字符串表示，表示方式如下：

前十个字符是乘客的手机号码。
接下来的一个字符是乘客的性别。
接下来两个字符是乘客的年龄。
最后两个字符是乘客的座位号。

请你返回乘客中年龄 严格大于 60 岁 的人数。

示例 1：

输入：details = ["7868190130M7522","5303914400F9211","9273338290F4010"]
输出：2
解释：下标为 0 ，1 和 2 的乘客年龄分别为 75 ，92 和 40 。所以有 2 人年龄大于 60 岁。

示例 2：

输入：details = ["1313579440F2036","2921522980M5644"]
输出：0
解释：没有乘客的年龄大于 60 岁。

提示：

1 <= details.length <= 100
details[i].length == 15
details[i] 中的数字只包含 '0' 到 '9' 。
details[i][10] 是 'M' ，'F' 或者 'O' 之一。
所有乘客的手机号码和座位号互不相同。

lightbulb

解题思路

方法一：遍历计数

我们可以遍历 details 中的每个字符串 $x$ ，并将 $x$ 的第 $12$ 和第 $13$ 个字符（下标为 $11$ , $12$ ）转换为整数，判断是否大于 $60$ ，如果是则将答案加一。

遍历结束后，返回答案即可。

时间复杂度 $O(n)$ ，其中 $n$ 是 details 的长度。空间复杂度 $O(1)$ 。

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2

3

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class Solution:
    def countSeniors(self, details: List[str]) -> int:
        return sum(int(x[11:13]) > 60 for x in details)

speed

复杂度分析

指标	值
时间	O(n)
空间	O(1)

psychology

面试官常问的追问

外企场景

question_mark
The candidate should focus on efficiently parsing and comparing the age values.
question_mark
A clear understanding of string indexing and conversion to integers is essential for solving this problem.
question_mark
The candidate must handle edge cases, such as when no passengers are older than 60.

warning

常见陷阱

外企场景

error
Incorrectly handling the substring extraction for the age (indexing issues).
error
Forgetting to convert the age from a string to an integer before comparison.
error
Overcomplicating the solution by introducing unnecessary steps or data structures.

swap_horiz

进阶变体

外企场景

arrow_right_alt
Modify the problem to count passengers over a different age threshold (e.g., 50 or 70).
arrow_right_alt
Handle cases where the passenger details contain invalid or corrupted data (e.g., malformed strings).
arrow_right_alt
Implement a more complex filtering system based on other passenger details, such as gender or seat number.

help

常见问题

外企场景

继续练习

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