add: leetcode 0520 readme

Author: tphyhFighting

leetcode/0520.Detect-Capital/README.md

@@ -0,0 +1,65 @@
+# [520. Detect Capital](https://leetcode-cn.com/problems/detect-capital/)
+
+
+## 题目
+
+We define the usage of capitals in a word to be right when one of the following cases holds:
+
+All letters in this word are capitals, like "USA".
+
+All letters in this word are not capitals, like "leetcode".
+
+Only the first letter in this word is capital, like "Google".
+
+Given a string word, return true if the usage of capitals in it is right.
+
+**Example 1:**
+
+```
+Input: word = "USA"
+Output: true
+```
+
+**Example 2:**
+
+```
+Input: word = "FlaG"
+Output: false
+```
+
+**Constraints:**
+
+- 1 <= word.length <= 100
+- word consists of lowercase and uppercase English letters.
+
+## 题目大意
+
+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" 。
+单词中所有字母都不是大写，比如 "leetcode" 。
+如果单词不只含有一个字母，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 。
+
+## 解题思路
+
+- 把word分别转换为全部小写wLower，全部大写wUpper，首字母大写的字符串wCaptial
+- 判断word是否等于wLower,wUpper,wCaptial中的一个，如果是返回true，否则返回false
+
+## 代码
+```go
+package leetcode
+
+import "strings"
+
+func detectCapitalUse(word string) bool {
+	wLower := strings.ToLower(word)
+	wUpper := strings.ToUpper(word)
+	wCaptial := strings.ToUpper(string(word[0])) + strings.ToLower(string(word[1:]))
+	if wCaptial == word || wLower == word || wUpper == word {
+		return true
+	}
+	return false
+}
+```