520. 检查单词大小写的合法性 Detect Capital

Given a word, you need to judge whether the usage of capitals in it is right or not.

We define the usage of capitals in a word to be right when one of the following cases holds:

1. All letters in this word are capitals, like "USA".
2. All letters in this word are not capitals, like "leetcode".
3. Only the first letter in this word is capital if it has more than one letter, like "Google".

Otherwise, we define that this word doesn't use capitals in a right way.

Example 1:

Input: "USA"
Output: True

Example 2:

Input: "FlaG"
Output: False

Note: The input will be a non-empty word consisting of uppercase and lowercase latin letters.

解法：三种合法情况：全大写，全小写，首字母大写其余小写

public class Solution {
    public bool DetectCapitalUse(string word) {
		string upCopy = word.ToUpper();
		string lowCopy = word.ToLower();
		if (word == upCopy || word == lowCopy) {
			return true;
		}
		string first = word.Substring(0, 1);
		string last = word.Substring(1, word.Length - 1);
		if (first.ToUpper() == first && last.ToLower() == last) {
			return true;
		}
		return false;
    }
}

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