Add solution #4

Author: JoshCrozier

README.md

@@ -6,6 +6,7 @@
 
 |#|Title|Difficulty|
 |:---|:---|:---|
+4|[Median of Two Sorted Arrays](./0004-median-of-two-sorted-arrays.js)|Hard|
 36|[Valid Sudoku](./0036-valid-sudoku.js)|Medium|
 58|[Length of Last Word](./0058-length-of-last-word.js)|Easy|
 151|[Reverse Words in a String](./0151-reverse-words-in-a-string.js)|Medium|

solutions/0004-median-of-two-sorted-arrays.js

@@ -0,0 +1,50 @@
+/**
+ * 4. Median of Two Sorted Arrays
+ * https://leetcode.com/problems/median-of-two-sorted-arrays/
+ * Difficulty: Hard
+ *
+ * There are two sorted arrays nums1 and nums2 of size m and n respectively.
+ *
+ * Find the median of the two sorted arrays.
+ * The overall run time complexity should be O(log (m+n)).
+ *
+ * You may assume nums1 and nums2 cannot be both empty.
+ */
+
+/**
+ * @param {number[]} nums1
+ * @param {number[]} nums2
+ * @return {number}
+ */
+var findMedianSortedArrays = function(nums1, nums2) {
+  const total = nums1.length + nums2.length;
+  const limit = Math.floor(total / 2) + 1;
+  let i = 0, j = 0, prev, last
+
+  while(i + j < limit) {
+    if (last !== undefined) {
+      prev = last;
+    }
+    if (nums1[i] < nums2[j] || j === nums2.length) {
+      last = nums1[i++];
+    } else {
+      last = nums2[j++];
+    }
+  }
+
+  return total % 2 === 0 ? (prev + last) / 2 : last;
+};
+
+// shorter/readable alternative with higher time complexity:
+/**
+ * @param {number[]} nums1
+ * @param {number[]} nums2
+ * @return {number}
+ */
+var findMedianSortedArrays = function(nums1, nums2) {
+  const sorted = [...nums1, ...nums2].sort((a, b) => a - b);
+  const index = Math.floor((sorted.length - 1) / 2);
+  return sorted.length % 2 === 0
+    ? (sorted[index] + sorted[index + 1]) / 2
+    : sorted[index];
+};