Next greater element

data_structures/arrays/next_greater_element.rb

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+# 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.
+
+# @param {Integer[]} nums1
+# @param {Integer[]} nums2
+# @return {Integer[]}
+def next_greater_element(nums1, nums2)
+  nums1.each_with_index do |value, pointer1|
+    max = 0
+    pos_nums2 = nums2.find_index(value)
+
+    nums2[pos_nums2..nums2.count].each do |value|
+      if value > nums1[pointer1]
+        max = value
+        break
+      end
+    end
+
+    nums1[pointer1] = (nums1[pointer1] < 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]