Maximum number by changing a 6 to a 9

12th exercise - #1323
https://leetcode.com/problems/maximum-69-number/submissions/

sixToNine.js

@@ -0,0 +1,45 @@
+/*
+Given a positive integer num consisting only of digits 6 and 9.
+
+Return the maximum number you can get by changing at most one digit (6 becomes 9, and 9 becomes 6).
+
+Example 1:
+
+Input: num = 9669
+Output: 9969
+Explanation: 
+Changing the first digit results in 6669.
+Changing the second digit results in 9969.
+Changing the third digit results in 9699.
+Changing the fourth digit results in 9666. 
+The maximum number is 9969.
+Example 2:
+
+Input: num = 9996
+Output: 9999
+Explanation: Changing the last digit 6 to 9 results in the maximum number.
+Example 3:
+
+Input: num = 9999
+Output: 9999
+Explanation: It is better not to apply any change.
+ 
+
+Constraints:
+
+1 <= num <= 10^4
+num's digits are 6 or 9.
+*/
+
+//Answer//
+/**
+ * @param {number} num
+ * @return {number}
+ */
+var maximum69Number  = function(num) {
+    if (num.toString().indexOf('6')===-1){return num}else{
+        let A = [...num+''];
+        A.splice(A.indexOf('6'),1,'9');
+        return Number(A.join(''))
+    }  
+};