leetcode-962 Maximum width ramp

Author: kumar91gopi

README.md

@@ -320,6 +320,8 @@ solution of many challenges of [Leetcode](https://leetcode.com/), [Exercism](htt
 ## [LeetCode](https://leetcode.com/problems)
 1. [Insert Delete GetRandom in O(1)](https://github.com/kumar91gopi/Algorithms-and-Data-Structures-in-Ruby/blob/master/leetcode/insert_delete_get_random_o1.rb)
 2. [Binary Tree Level order Traversal](https://github.com/kumar91gopi/Algorithms-and-Data-Structures-in-Ruby/blob/master/leetcode/binary_tree_level_order_traversal.rb)
+3. [Maximum Width Ramp (Leetcode-962)](https://github.com/kumar91gopi/Algorithms-and-Data-Structures-in-Ruby/blob/master/leetcode/maximum_width_ramp.rb)
+
 
 <a name="grind-75"/>
 

leetcode/maximum_width_ramp.rb

@@ -0,0 +1,32 @@
+=begin
+A ramp in an integer array nums is a pair (i, j) for which i < j and nums[i] <= nums[j]. The width of such a ramp is j - i.
+Given an integer array nums, return the maximum width of a ramp in nums. If there is no ramp in nums, return 0.
+Example 1:
+Input: nums = [6,0,8,2,1,5]
+Output: 4
+Explanation: The maximum width ramp is achieved at (i, j) = (1, 5): nums[1] = 0 and nums[5] = 5.
+Example 2:
+Input: nums = [9,8,1,0,1,9,4,0,4,1]
+Output: 7
+Explanation: The maximum width ramp is achieved at (i, j) = (2, 9): nums[2] = 1 and nums[9] = 1.
+
+#Problem(962): https://leetcode.com/problems/maximum-width-ramp/description/
+=end
+
+# Solution 1 (Using monotonic stack)
+# @param {Integer[]} nums
+# @return {Integer}
+def max_width_ramp(nums)
+    decreasing_stack = [0]
+    for i in 1...nums.length
+       decreasing_stack.append(i) if nums[decreasing_stack[-1]]>nums[i]                         
+    end
+
+    max_width = 0
+    (nums.length-1).downto(0) do |j|
+        until decreasing_stack.empty? || nums[decreasing_stack[-1]]>nums[j]
+            max_width = [max_width, j-decreasing_stack.pop].max
+        end
+    end
+    max_width   
+end