Add collatz-conjecture (#206)

Author: BNAndras

config.json

@@ -82,6 +82,14 @@
         "prerequisites": [],
         "difficulty": 3
       },
+      {
+        "slug": "collatz-conjecture",
+        "name": "Collatz Conjecture",
+        "uuid": "4eed1dde-4e87-4cbf-834e-71da55128215",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 2
+      },
       {
         "slug": "difference-of-squares",
         "name": "Difference of Squares",

exercises/practice/collatz-conjecture/.docs/instructions.md

@@ -0,0 +1,29 @@
+# Instructions
+
+The Collatz Conjecture or 3x+1 problem can be summarized as follows:
+
+Take any positive integer n.
+If n is even, divide n by 2 to get n / 2.
+If n is odd, multiply n by 3 and add 1 to get 3n + 1.
+Repeat the process indefinitely.
+The conjecture states that no matter which number you start with, you will always reach 1 eventually.
+
+Given a number n, return the number of steps required to reach 1.
+
+## Examples
+
+Starting with n = 12, the steps would be as follows:
+
+0. 12
+1. 6
+2. 3
+3. 10
+4. 5
+5. 16
+6. 8
+7. 4
+8. 2
+9. 1
+
+Resulting in 9 steps.
+So for input n = 12, the return value would be 9.

exercises/practice/collatz-conjecture/.meta/config.json

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "BNAndras"
+  ],
+  "files": {
+    "solution": [
+      "collatz_conjecture.vim"
+    ],
+    "test": [
+      "collatz_conjecture.vader"
+    ],
+    "example": [
+      ".meta/example.vim"
+    ]
+  },
+  "blurb": "Calculate the number of steps to reach 1 using the Collatz conjecture.",
+  "source": "An unsolved problem in mathematics named after mathematician Lothar Collatz",
+  "source_url": "https://en.wikipedia.org/wiki/3x_%2B_1_problem"
+}

exercises/practice/collatz-conjecture/.meta/example.vim

@@ -0,0 +1,19 @@
+function! Steps(number) abort
+  if a:number < 1
+    throw 'Only positive integers are allowed'
+  endif
+
+  let l:step = 0
+  let l:working = a:number
+  while l:working != 1
+    if l:working % 2 == 0
+      let l:working /= 2
+    else
+      let l:working = 3 * l:working + 1
+    endif
+  
+    let l:step += 1
+  endwhile
+  
+  return l:step
+endfunction

exercises/practice/collatz-conjecture/.meta/tests.toml

@@ -0,0 +1,38 @@
+# This is an auto-generated file.
+#
+# Regenerating this file via `configlet sync` will:
+# - Recreate every `description` key/value pair
+# - Recreate every `reimplements` key/value pair, where they exist in problem-specifications
+# - Remove any `include = true` key/value pair (an omitted `include` key implies inclusion)
+# - Preserve any other key/value pair
+#
+# As user-added comments (using the # character) will be removed when this file
+# is regenerated, comments can be added via a `comment` key.
+
+[540a3d51-e7a6-47a5-92a3-4ad1838f0bfd]
+description = "zero steps for one"
+
+[3d76a0a6-ea84-444a-821a-f7857c2c1859]
+description = "divide if even"
+
+[754dea81-123c-429e-b8bc-db20b05a87b9]
+description = "even and odd steps"
+
+[ecfd0210-6f85-44f6-8280-f65534892ff6]
+description = "large number of even and odd steps"
+
+[7d4750e6-def9-4b86-aec7-9f7eb44f95a3]
+description = "zero is an error"
+include = false
+
+[2187673d-77d6-4543-975e-66df6c50e2da]
+description = "zero is an error"
+reimplements = "7d4750e6-def9-4b86-aec7-9f7eb44f95a3"
+
+[c6c795bf-a288-45e9-86a1-841359ad426d]
+description = "negative value is an error"
+include = false
+
+[ec11f479-56bc-47fd-a434-bcd7a31a7a2e]
+description = "negative value is an error"
+reimplements = "c6c795bf-a288-45e9-86a1-841359ad426d"

exercises/practice/collatz-conjecture/collatz_conjecture.vader

@@ -0,0 +1,32 @@
+
+Execute (zero steps for one):
+  let g:number = 1
+  let g:expected = 0
+  AssertEqual g:expected, Steps(g:number)
+
+Execute (divide if even):
+  let g:number = 16
+  let g:expected = 4
+  AssertEqual g:expected, Steps(g:number)
+
+Execute (even and odd steps):
+  let g:number = 12
+  let g:expected = 9
+  AssertEqual g:expected, Steps(g:number)
+
+Execute (large number of even and odd steps):
+  let g:number = 1000000
+  let g:expected = 152
+  AssertEqual g:expected, Steps(g:number)
+
+Execute (zero is an error):
+  let g:number = 0
+  let g:expected = "Only positive integers are allowed"
+  AssertThrows call Steps(g:number)
+  AssertEqual g:expected, g:vader_exception
+
+Execute (negative value is an error):
+  let g:number = -15
+  let g:expected = "Only positive integers are allowed"
+  AssertThrows call Steps(g:number)
+  AssertEqual g:expected, g:vader_exception

exercises/practice/collatz-conjecture/collatz_conjecture.vim

@@ -0,0 +1,16 @@
+"
+" Returns the number of steps to reach 1 for a given number
+" using the Collatz Conjecture or 3x+1 problem.
+" Throws an error if input is less than 1.
+"
+" Example:
+"
+"   :echo Steps(16)
+"   4
+"
+"   :echo Steps(-1)
+"   E605: Exception not caught: Only positive integers are allowed
+"
+function! Steps(number) abort
+  " your solution goes here
+endfunction