feat: add golang solutions to lc problem: No.0389 (doocs#885)

Author: guowei-gong

solution/0300-0399/0389.Find the Difference/README.md

@@ -192,6 +192,24 @@ char findTheDifference(char *s, char *t) {
 }
 ```
 
+### **Go**
+
+```go
+func findTheDifference(s, t string) byte {
+	cnt := [26]int{}
+	for _, ch := range s {
+		cnt[ch-'a']++
+	}
+	for i := 0; ; i++ {
+		ch := t[i]
+		cnt[ch-'a']--
+		if cnt[ch-'a'] < 0 {
+			return ch
+		}
+	}
+}
+```
+
 ### **...**
 
 ```

solution/0300-0399/0389.Find the Difference/README_EN.md

@@ -168,6 +168,24 @@ char findTheDifference(char *s, char *t) {
 }
 ```
 
+### **Go**
+
+```go
+func findTheDifference(s, t string) byte {
+	cnt := [26]int{}
+	for _, ch := range s {
+		cnt[ch-'a']++
+	}
+	for i := 0; ; i++ {
+		ch := t[i]
+		cnt[ch-'a']--
+		if cnt[ch-'a'] < 0 {
+			return ch
+		}
+	}
+}
+```
+
 ### **...**
 
 ```

solution/0300-0399/0389.Find the Difference/Solution.go

@@ -0,0 +1,13 @@
+func findTheDifference(s, t string) byte {
+	cnt := [26]int{}
+	for _, ch := range s {
+		cnt[ch-'a']++
+	}
+	for i := 0; ; i++ {
+		ch := t[i]
+		cnt[ch-'a']--
+		if cnt[ch-'a'] < 0 {
+			return ch
+		}
+	}
+}