What are the rules for correct capital usage in the Detect Capital problem?

The correct capital usage can be: all letters are uppercase, all are lowercase, or only the first letter is uppercase and the rest are lowercase.

How can I check if a word is in title case for Detect Capital?

You can use Python's `.istitle()` method to check if only the first letter of the word is uppercase and all subsequent letters are lowercase.

Is there a time complexity advantage to checking all lowercase or all uppercase first?

Yes, checking if a word is fully lowercase or uppercase can short-circuit the process and quickly determine validity without needing further checks.

What should I do if I get mixed case words like 'FlaG' in the Detect Capital problem?

Mixed case words like 'FlaG' do not satisfy any of the three valid capitalization rules and should return `false`.

What is the space complexity of solving Detect Capital?

The space complexity is O(1), as no extra space is used beyond simple variable checks for capitalization.

#520

Easy

auto_awesomeString-driven solution strategy

LeetCode 题解工作台

检测大写字母

我们定义，在以下情况时，单词的大写用法是正确的：全部字母都是大写，比如 "USA" 。所有字母都不是大写，比如 "leetcode" 。只有首字母大写，比如 "Google" 。给你一个字符串 word 。如果大写用法正确，返回 true ；否则，返回 false 。示例 1：输入： …

字符串

题目描述

我们定义，在以下情况时，单词的大写用法是正确的：

全部字母都是大写，比如 "USA" 。
所有字母都不是大写，比如 "leetcode" 。
只有首字母大写，比如 "Google" 。

给你一个字符串 word 。如果大写用法正确，返回 true ；否则，返回 false 。

示例 1：

输入：word = "USA"
输出：true

示例 2：

输入：word = "FlaG"
输出：false

提示：

1 <= word.length <= 100
word 由小写和大写英文字母组成

lightbulb

解题思路

方法一：统计大写字母的个数

我们可以统计字符串中大写字母的个数，然后根据大写字母的个数判断是否符合题目要求。

如果大写字母的个数为 0 或者等于字符串的长度，那么返回 true。
如果大写字母的个数为 1 并且第一个字母是大写字母，那么返回 true。
否则返回 false。

时间复杂度 $O(n)$ ，其中 $n$ 为字符串 word 的长度。空间复杂度 $O(1)$ 。

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class Solution:
    def detectCapitalUse(self, word: str) -> bool:
        cnt = sum(c.isupper() for c in word)
        return cnt == 0 or cnt == len(word) or (cnt == 1 and word[0].isupper())

speed

复杂度分析

指标	值
时间	Depends on the final approach
空间	Depends on the final approach

psychology

面试官常问的追问

外企场景

question_mark
Candidate efficiently identifies string-driven checks to validate each capitalization rule.
question_mark
Candidate might miss the importance of using Python's string methods like `.upper()` and `.istitle()`.
question_mark
Candidate could misinterpret the rules, for example, returning true for mixed capitalization where it's invalid.

warning

常见陷阱

外企场景

error
Confusing mixed capital cases (like 'FlaG') as valid when it does not meet any of the rules.
error
Overcomplicating the solution by adding unnecessary conditions or checks.
error
Forgetting to handle edge cases such as very short strings like 'A' or 'a'.

swap_horiz

进阶变体

外企场景

arrow_right_alt
Check for variations in capitalization beyond the basic three rules (e.g., alternating case).
arrow_right_alt
Handle words with punctuation or non-alphabetical characters (though these are out of scope for this problem).
arrow_right_alt
Extend the solution to work with multiple strings or inputs in batch processing.

help

常见问题

外企场景

继续练习

#521 最长特殊序列 Ⅰ #522 最长特殊序列 II #516 最长回文子序列