feat: add solutions to lc problem: No.2047

solution/2000-2099/2047.Number of Valid Words in a Sentence/README.md

@@ -77,7 +77,25 @@ tags:
 
 <!-- solution:start -->
 
-### 方法一
+### 方法一：模拟
+
+我们首先将句子按空格分割成单词，然后对每个单词进行检查，判断是否为有效单词。
+
+对于每个单词，我们可以使用一个布尔变量 $\textit{st}$ 来记录是否已经出现过连字符，然后遍历单词中的每个字符，根据题目描述的规则进行判断。
+
+对于每个字符 $s[i]$，我们有以下几种情况：
+
+-   如果 $s[i]$ 是数字，那么 $s$ 不是有效单词，直接返回 $\text{false}$；
+-   如果 $s[i]$ 是标点符号（'!'、'.'、','）且 $i < \text{len}(s) - 1$，那么 $s$ 不是有效单词，直接返回 $\text{false}$；
+-   如果 $s[i]$ 是连字符，那么我们需要判断是否满足以下条件：
+    -   连字符只能出现一次；
+    -   连字符不能出现在单词的开头或结尾；
+    -   连字符两侧必须是字母；
+-   如果 $s[i]$ 是字母，那么我们不需要做任何处理。
+
+最后，我们统计出句子中的有效单词数即可。
+
+时间复杂度 $O(n)$，空间复杂度 $O(n)$。其中 $n$ 是句子的长度。
 
 <!-- tabs:start -->
 
@@ -86,24 +104,23 @@ tags:
 ```python
 class Solution:
     def countValidWords(self, sentence: str) -> int:
-        def check(token):
-            hyphen = False
-            for i, c in enumerate(token):
-                if c.isdigit() or (c in '!.,' and i < len(token) - 1):
+        def check(s: str) -> bool:
+            st = False
+            for i, c in enumerate(s):
+                if c.isdigit() or (c in "!.," and i < len(s) - 1):
                     return False
-                if c == '-':
+                if c == "-":
                     if (
-                        hyphen
-                        or i == 0
-                        or i == len(token) - 1
-                        or not token[i - 1].islower()
-                        or not token[i + 1].islower()
+                        st
+                        or i in (0, len(s) - 1)
+                        or not s[i - 1].isalpha()
+                        or not s[i + 1].isalpha()
                     ):
                         return False
-                    hyphen = True
+                    st = True
             return True
 
-        return sum(check(token) for token in sentence.split())
+        return sum(check(s) for s in sentence.split())
 ```
 
 #### Java
@@ -112,76 +129,142 @@ class Solution:
 class Solution {
     public int countValidWords(String sentence) {
         int ans = 0;
-        for (String token : sentence.split(" ")) {
-            if (check(token)) {
-                ++ans;
-            }
+        for (String s : sentence.split(" ")) {
+            ans += check(s.toCharArray());
         }
         return ans;
     }
 
-    private boolean check(String token) {
-        int n = token.length();
-        if (n == 0) {
-            return false;
+    private int check(char[] s) {
+        if (s.length == 0) {
+            return 0;
         }
-        boolean hyphen = false;
-        for (int i = 0; i < n; ++i) {
-            char c = token.charAt(i);
-            if (Character.isDigit(c) || (i < n - 1 && (c == '!' || c == '.' || c == ','))) {
-                return false;
+        boolean st = false;
+        for (int i = 0; i < s.length; ++i) {
+            if (Character.isDigit(s[i])) {
+                return 0;
+            }
+            if ((s[i] == '!' || s[i] == '.' || s[i] == ',') && i < s.length - 1) {
+                return 0;
             }
-            if (c == '-') {
-                if (hyphen || i == 0 || i == n - 1 || !Character.isLetter(token.charAt(i - 1))
-                    || !Character.isLetter(token.charAt(i + 1))) {
-                    return false;
+            if (s[i] == '-') {
+                if (st || i == 0 || i == s.length - 1) {
+                    return 0;
                 }
-                hyphen = true;
+                if (!Character.isAlphabetic(s[i - 1]) || !Character.isAlphabetic(s[i + 1])) {
+                    return 0;
+                }
+                st = true;
             }
         }
-        return true;
+        return 1;
     }
 }
 ```
 
-#### TypeScript
+#### C++
 
-```ts
-function countValidWords(sentence: string): number {
-    let words = sentence.trim().split(/\s+/);
-    let ans = 0;
-    for (let word of words) {
-        if (isValied(word)) {
-            ans++;
+```cpp
+class Solution {
+public:
+    int countValidWords(string sentence) {
+        auto check = [](const string& s) -> int {
+            bool st = false;
+            for (int i = 0; i < s.length(); ++i) {
+                if (isdigit(s[i])) {
+                    return 0;
+                }
+                if ((s[i] == '!' || s[i] == '.' || s[i] == ',') && i < s.length() - 1) {
+                    return 0;
+                }
+                if (s[i] == '-') {
+                    if (st || i == 0 || i == s.length() - 1) {
+                        return 0;
+                    }
+                    if (!isalpha(s[i - 1]) || !isalpha(s[i + 1])) {
+                        return 0;
+                    }
+                    st = true;
+                }
+            }
+            return 1;
+        };
+
+        int ans = 0;
+        stringstream ss(sentence);
+        string s;
+        while (ss >> s) {
+            ans += check(s);
         }
+        return ans;
     }
-    return ans;
+};
+```
+
+#### Go
+
+```go
+func countValidWords(sentence string) (ans int) {
+	check := func(s string) int {
+		if len(s) == 0 {
+			return 0
+		}
+		st := false
+		for i, r := range s {
+			if unicode.IsDigit(r) {
+				return 0
+			}
+			if (r == '!' || r == '.' || r == ',') && i < len(s)-1 {
+				return 0
+			}
+			if r == '-' {
+				if st || i == 0 || i == len(s)-1 {
+					return 0
+				}
+				if !unicode.IsLetter(rune(s[i-1])) || !unicode.IsLetter(rune(s[i+1])) {
+					return 0
+				}
+				st = true
+			}
+		}
+		return 1
+	}
+	for _, s := range strings.Fields(sentence) {
+		ans += check(s)
+	}
+	return ans
 }
+```
+
+#### TypeScript
 
-function isValied(str: string): boolean {
-    let n = str.length;
-    let hasLine = false;
-    for (let i = 0; i < n; i++) {
-        const char = str.charAt(i);
-        if (/^[0-9]$/.test(char)) {
-            return false;
+```ts
+function countValidWords(sentence: string): number {
+    const check = (s: string): number => {
+        if (s.length === 0) {
+            return 0;
         }
-        if (char == '-') {
-            if (hasLine) return false;
-            else {
-                hasLine = true;
+        let st = false;
+        for (let i = 0; i < s.length; ++i) {
+            if (/\d/.test(s[i])) {
+                return 0;
             }
-            let pre = str.charAt(i - 1),
-                post = str.charAt(i + 1);
-            if (!/^[a-z]$/g.test(pre) || !/^[a-z]$/g.test(post)) {
-                return false;
+            if (['!', '.', ','].includes(s[i]) && i < s.length - 1) {
+                return 0;
+            }
+            if (s[i] === '-') {
+                if (st || [0, s.length - 1].includes(i)) {
+                    return 0;
+                }
+                if (!/[a-zA-Z]/.test(s[i - 1]) || !/[a-zA-Z]/.test(s[i + 1])) {
+                    return 0;
+                }
+                st = true;
             }
         }
-        if (/^[\!\.\,\s]$/.test(char) && i != n - 1) {
-            return false;
-        }
-    }
-    return true;
+        return 1;
+    };
+    return sentence.split(/\s+/).reduce((acc, s) => acc + check(s), 0);
 }
 ```