70 && 83 && 88

Climbing_Stairs.rb

@@ -0,0 +1,37 @@
+#
+# @lc app=leetcode id=70 lang=ruby
+#
+# [70] Climbing Stairs
+#
+# https://leetcode.com/problems/climbing-stairs/description/
+#
+# You are climbing a stair case. It takes n steps to reach to the top.
+#
+# Each time you can either climb 1 or 2 steps. In how many distinct
+# ways can you climb to the top?
+#
+# Note: Given n will be a positive integer.
+#
+# Example 1:
+#
+# Input: 2
+# Output: 2
+# Explanation: There are two ways to climb to the top.
+# 1. 1 step + 1 step
+# 2. 2 steps
+#
+# Example 2:
+#
+# Input: 3
+# Output: 3
+# Explanation: There are three ways to climb to the top.
+# 1. 1 step + 1 step + 1 step
+# 2. 1 step + 2 steps
+# 3. 2 steps + 1 step
+
+
+# @param {Integer} n
+# @return {Integer}
+def climb_stairs(n)
+  Hash.new { |h, k| h[k] = h[k-1] + h[k-2] }.merge({1=>1, 2=>2})[n]
+end

Merge_Sorted_Array.rb

@@ -0,0 +1,24 @@
+# @param {Integer[]} nums1
+# @param {Integer} m
+# @param {Integer[]} nums2
+# @param {Integer} n
+# @return {Void} Do not return anything, modify nums1 in-place instead.
+def merge(nums1, m, nums2, n)
+    i, j, k = n - 1, m - 1, nums1.size - 1
+
+    while i >= 0
+        if j < 0
+            nums1[k] = nums2[i]
+            i -= 1
+        elsif nums1[j] > nums2[i]
+            nums1[k] = nums1[j]
+            j -= 1
+        else
+            nums1[k] = nums2[i]
+            i -= 1
+        end   
+        k -= 1
+    end
+
+    nums1
+end

Remove_Duplicates_from_Sorted_Linked_List.rb

@@ -0,0 +1,13 @@
+def delete_duplicates(head)
+    cursor = head
+
+  while cursor and cursor.next
+    if cursor.next.val == cursor.val
+      cursor.next = cursor.next.next
+    else
+      cursor = cursor.next
+    end
+  end
+
+  head
+end