add: reverse integer

Author: ongch

LeetcodeProblems/Algorithms/Reverse_Integer.js

@@ -0,0 +1,46 @@
+/**
+Reverse Integer
+https://leetcode.com/problems/reverse-integer/
+
+Given a signed 32-bit integer x, return x with its digits reversed. If reversing x causes the value to go outside the signed 32-bit integer range [-231, 231 - 1], then return 0.
+
+Assume the environment does not allow you to store 64-bit integers (signed or unsigned).
+
+Example 1:
+Input: x = 123
+Output: 321
+
+Example 2:
+Input: x = -123
+Output: -321
+
+Example 3:
+Input: x = 120
+Output: 21
+
+ */
+
+/**
+ * @param {number} x
+ * @return {number}
+ */
+var reverseInteger = function(x) {
+  const sign = x >= 0 ? 1 : -1;
+  
+  let baseNum = sign * x;
+  let builder = 0;
+  
+  while (baseNum > 0) {
+    const digit = baseNum % 10;
+    builder = builder * 10 + digit;
+    baseNum = (baseNum / 10) | 0;
+  }
+  
+  builder *= sign;
+  
+  const isWithinRange = (builder >= -Math.pow(2, 31) && builder <= Math.pow(2, 31) - 1);
+  
+  return isWithinRange ? builder : 0;
+};
+
+module.exports.reverseInteger = reverseInteger;

README.md

@@ -62,6 +62,7 @@ To run a specific problem in your console run  `node <problem_file_path>` (e.g.
 | [Construct Binary Tree from Preorder and Inorder Traversal ](/LeetcodeProblems/Algorithms/Construct_Binary_Tree_from_Preorder_and_Inorder_Traversal.js)   | Medium | https://leetcode.com/problems/construct-binary-tree-from-preorder-and-inorder-traversal/ | 
 | [Lowest Common Ancestor of a Binary Tree ](/LeetcodeProblems/Algorithms/Lowest_Common_Ancestor_of_a_Binary_Tree.js) | Medium | https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-tree/ |
 | [Maximum Sum of an Hourglass](/LeetcodeProblems/Algorithms/Maximise_Hour_Glass_Sum.js)                          | Medium | https://leetcode.com/problems/maximum-sum-of-an-hourglass/ |
+| [Reverse Integer](/LeetcodeProblems/Algorithms/Reverse_Integer.js)                          | Medium | https://leetcode.com/problems/reverse-integer/ |
 | [Flood Fill ](/LeetcodeProblems/Algorithms/Flood_Fill.js)                                                       | Easy   | https://leetcode.com/problems/flood-fill/ |
 | [Implement stack using queues ](/LeetcodeProblems/Algorithms/Implement_stack_using_queues.js)                   | Easy   | https://leetcode.com/problems/implement-stack-using-queues/ |
 | [Number of Segments in a String ](/LeetcodeProblems/Algorithms/Number_of_Segments_in_a_String.js)               | Easy   | https://leetcode.com/problems/number-of-segments-in-a-string/ |