update: 2 solutions

Author: hijiangtao

README.md

@@ -2,17 +2,19 @@
 
 This is the solution collection of my LeetCode problems, most of them are programmed in JavaScript.
 
-Progress: 9/
+Progress: 12/
 
 | ID | Title | Solution | Difficulty |
 |---| ----- | -------- | ---------- |
 |1|[Two Sum](https://leetcode.com/problems/two-sum/) | [JavaScript](./src/two-sum/res.js)|Easy|
 |2|[Add Two Numbers](https://leetcode.com/problems/add-two-numbers/) | [JavaScript](./src/add-two-numbers/res.js)|Medium|
+|66|[Plus One](https://leetcode.com/problems/plus-one/) | [JavaScript](./src/plus-one/res.js)|Easy|
 |175|[Combine Two Tables](https://leetcode.com/problems/combine-two-tables/)| [SQL](./src/combine-two-tables/res.txt)|Easy|
 |176|[Second Highest Salary](https://leetcode.com/problems/second-highest-salary/)| [SQL](./src/second-highest-salary/res.txt)|Easy|
 |177|[Nth Highest Salary](https://leetcode.com/problems/nth-highest-salary/)| [SQL](./src/nth-highest-salary/res.txt)|Medium|
 |181|[Employees Earning More Than Their Managers](https://leetcode.com/problems/employees-earning-more-than-their-managers/) | [SQL](./src/employees-earning-more-than-their-managers/res.txt)|Easy|
 |182|[Duplicate Emails](https://leetcode.com/problems/duplicate-emails/) | [SQL](./src/duplicate-emails/res.txt)|Easy|
 |184|[Department Highest Salary](https://leetcode.com/problems/department-highest-salary/) | [SQL](./src/department-highest-salary/res.txt)|Medium|
 |197|[Rising Temperature](https://leetcode.com/problems/rising-temperature/) | [SQL](./src/rising-temperature/res.txt)|Easy|
+|342|[Power of Four](https://leetcode.com/problems/power-of-four/) | [JavaScript](./src/power-of-four/res.js)|Easy|
 |434|[Number of Segments in a String](https://leetcode.com/problems/number-of-segments-in-a-string/) | [JavaScript](./src/number-of-segments-in-a-string/res.js)|Easy|

src/plus-one/res.js

@@ -0,0 +1,38 @@
+/**
+ * Given a non-negative integer represented as a non-empty array of digits, plus one to the integer.
+ * 
+ * You may assume the integer do not contain any leading zero, except the number 0 itself.
+ * 
+ * The digits are stored such that the most significant digit is at the head of the list.
+ * 
+ * res.js
+ * @authors Joe Jiang ([email protected])
+ * @date    2017-02-18 19:41:09
+ * @version $Id$
+ */
+
+/**
+ * @param {number[]} digits
+ * @return {number[]}
+ */
+let plusOne = function(digits) {
+   let carrybit = 1,
+       res = [];
+   
+   for (let i = digits.length - 1; i >= 0; i--) {
+    let currentval = digits[i] + carrybit;
+    if (currentval>9) {
+    	carrybit=1;
+    	currentval%=10;
+    } else {
+    	carrybit=0;
+    }
+    res.unshift(currentval)
+   }
+
+   if (carrybit===1) {
+   	res.unshift(1);
+   }
+
+   return res;
+};

src/power-of-four/res.js

@@ -0,0 +1,31 @@
+/**
+ * Given an integer (signed 32 bits), write a function to check whether it is a power of 4.
+ * 
+ * Example:
+ * 
+ * Given num = 16, return true. Given num = 5, return false.
+ * 
+ * Follow up: Could you solve it without loops/recursion?
+ *
+ * Hint: We know that if number is power of two, it satisfies that n & (n – 1) equals zero, that is: n & (n – 1) removes the least significant bit, leaving the number (that is power of two) zero. We also know that mathematically, 4^n - 1  can be divided by 3.
+ * 
+ * @authors Joe Jiang ([email protected])
+ * @date    2017-02-18 20:13:10
+ * @version $Id$
+ */
+
+/**
+ * @param {number} num
+ * @return {boolean}
+ */
+let isPowerOfFour = function(num) {
+    let compNum = num-1;
+    if (num<1 || num & compNum) {
+        return false;
+    }
+    if (compNum%3 !== 0) {
+        return false;
+    }
+    
+    return true;
+};