Merge pull request #126 from TheAlgorithms/next-greater-element

DIRECTORY.md

@@ -18,6 +18,7 @@
     * [Find The Highest Altitude](https://github.com/TheAlgorithms/Ruby/blob/master/data_structures/arrays/find_the_highest_altitude.rb)
     * [Fizz Buzz](https://github.com/TheAlgorithms/Ruby/blob/master/data_structures/arrays/fizz_buzz.rb)
     * [Get Products Of All Other Elements](https://github.com/TheAlgorithms/Ruby/blob/master/data_structures/arrays/get_products_of_all_other_elements.rb)
+    * [Next Greater Element](https://github.com/TheAlgorithms/Ruby/blob/master/data_structures/arrays/next_greater_element.rb)
     * [Remove Elements](https://github.com/TheAlgorithms/Ruby/blob/master/data_structures/arrays/remove_elements.rb)
     * [Richest Customer Wealth](https://github.com/TheAlgorithms/Ruby/blob/master/data_structures/arrays/richest_customer_wealth.rb)
     * [Shuffle Array](https://github.com/TheAlgorithms/Ruby/blob/master/data_structures/arrays/shuffle_array.rb)

data_structures/arrays/next_greater_element.rb

@@ -0,0 +1,64 @@
+# You are given two integer arrays nums1 and nums2 both of unique elements, where nums1 is a subset of nums2.
+#
+# Find all the next greater numbers for nums1's elements in the corresponding places of nums2.
+#
+# The Next Greater Number of a number x in nums1 is the first greater number to its right in nums2. If it does not exist, return -1 for this number.
+
+# Example 1:
+#
+# Input: nums1 = [4,1,2], nums2 = [1,3,4,2]
+# Output: [-1,3,-1]
+#
+# Explanation:
+# For number 4 in the first array, you cannot find the next greater number for it in the second array, so output -1.
+# For number 1 in the first array, the next greater number for it in the second array is 3.
+# For number 2 in the first array, there is no next greater number for it in the second array, so output -1.
+#
+# Example 2:
+#
+# Input: nums1 = [2,4], nums2 = [1,2,3,4]
+# Output: [3,-1]
+#
+# Explanation:
+# For number 2 in the first array, the next greater number for it in the second array is 3.
+# For number 4 in the first array, there is no next greater number for it in the second array, so output -1.
+
+# 
+# Approach: Brute Force
+# 
+
+# Complexity Analysis
+# 
+# Time complexity: O(m*n). The complete nums1 array (of size n) needs to be scanned for all the m elements of nums2 in the worst case.
+# Space complexity: O(1). No additional space since we're swapping elements in nums1 and returning the input array.
+
+# @param {Integer[]} nums1
+# @param {Integer[]} nums2
+# @return {Integer[]}
+def next_greater_element(nums1, nums2)
+  nums1.each_with_index do |nums1_value, pointer1|
+    max = 0
+    pos_nums2 = nums2.find_index(nums1_value)
+
+    nums2[pos_nums2..nums2.count].each do |nums2_value|
+      if nums2_value > nums1_value
+        max = nums2_value
+        break
+      end
+    end
+
+    nums1[pointer1] = (nums1_value < max ? max : -1)
+  end
+
+  nums1
+end
+
+nums1 = [4, 1, 2]
+nums2 = [1, 3, 4, 2]
+print next_greater_element(nums1, nums2)
+# Output: [-1,3,-1]
+
+nums1 = [2, 4]
+nums2 = [1, 2, 3, 4]
+print next_greater_element(nums1, nums2)
+# Output: [3,-1]