Add saddle-points

config.json

@@ -519,6 +519,14 @@
         "prerequisites": [],
         "difficulty": 2
       },
+      {
+        "slug": "saddle-points",
+        "name": "Saddle Points",
+        "uuid": "3abe4014-3f1d-4178-9b3a-bc0fff0f1322",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 2
+      },
       {
         "slug": "scrabble-score",
         "name": "Scrabble Score",

exercises/practice/saddle-points/.docs/instructions.md

@@ -0,0 +1,27 @@
+# Instructions
+
+Your task is to find the potential trees where you could build your tree house.
+
+The data company provides the data as grids that show the heights of the trees.
+The rows of the grid represent the east-west direction, and the columns represent the north-south direction.
+
+An acceptable tree will be the largest in its row, while being the smallest in its column.
+
+A grid might not have any good trees at all.
+Or it might have one, or even several.
+
+Here is a grid that has exactly one candidate tree.
+
+```text
+      ↓
+      1  2  3  4
+    |-----------
+  1 | 9  8  7  8
+→ 2 |[5] 3  2  4
+  3 | 6  6  7  1
+```
+
+- Row 2 has values 5, 3, 2, and 4. The largest value is 5.
+- Column 1 has values 9, 5, and 6. The smallest value is 5.
+
+So the point at `[2, 1]` (row: 2, column: 1) is a great spot for a tree house.

exercises/practice/saddle-points/.docs/introduction.md

@@ -0,0 +1,11 @@
+# Introduction
+
+You plan to build a tree house in the woods near your house so that you can watch the sun rise and set.
+
+You've obtained data from a local survey company that show the height of every tree in each rectangular section of the map.
+You need to analyze each grid on the map to find good trees for your tree house.
+
+A good tree is both:
+
+- taller than every tree to the east and west, so that you have the best possible view of the sunrises and sunsets.
+- shorter than every tree to the north and south, to minimize the amount of tree climbing.

exercises/practice/saddle-points/.meta/config.json

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "BNAndras"
+  ],
+  "files": {
+    "solution": [
+      "saddle-points.coffee"
+    ],
+    "test": [
+      "saddle-points.spec.coffee"
+    ],
+    "example": [
+      ".meta/example.coffee"
+    ]
+  },
+  "blurb": "Detect saddle points in a matrix.",
+  "source": "J Dalbey's Programming Practice problems",
+  "source_url": "https://users.csc.calpoly.edu/~jdalbey/103/Projects/ProgrammingPractice.html"
+}

exercises/practice/saddle-points/.meta/example.coffee

@@ -0,0 +1,19 @@
+SaddlePoints = (matrix) ->
+  return [] if matrix.length == 0
+
+  rows = matrix.length
+  columns = matrix[0].length
+
+  tallestInEachRow = matrix.map (row) => Math.max row...
+  shortestInEachColumn = [0...columns].map (c) ->
+    Math.min (matrix[r][c] for r in [0...rows])...
+
+  saddlePoints = []
+  for i in [0...rows]
+    for j in [0...columns]
+      current = matrix[i][j]
+      if current == tallestInEachRow[i] and current == shortestInEachColumn[j]
+        saddlePoints.push {row: i + 1, column: j + 1}
+  saddlePoints
+
+module.exports = SaddlePoints

exercises/practice/saddle-points/.meta/tests.toml

@@ -0,0 +1,37 @@
+# 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.
+
+[3e374e63-a2e0-4530-a39a-d53c560382bd]
+description = "Can identify single saddle point"
+
+[6b501e2b-6c1f-491f-b1bb-7f278f760534]
+description = "Can identify that empty matrix has no saddle points"
+
+[8c27cc64-e573-4fcb-a099-f0ae863fb02f]
+description = "Can identify lack of saddle points when there are none"
+
+[6d1399bd-e105-40fd-a2c9-c6609507d7a3]
+description = "Can identify multiple saddle points in a column"
+
+[3e81dce9-53b3-44e6-bf26-e328885fd5d1]
+description = "Can identify multiple saddle points in a row"
+
+[88868621-b6f4-4837-bb8b-3fad8b25d46b]
+description = "Can identify saddle point in bottom right corner"
+
+[5b9499ca-fcea-4195-830a-9c4584a0ee79]
+description = "Can identify saddle points in a non square matrix"
+
+[ee99ccd2-a1f1-4283-ad39-f8c70f0cf594]
+description = "Can identify that saddle points in a single column matrix are those with the minimum value"
+
+[63abf709-a84b-407f-a1b3-456638689713]
+description = "Can identify that saddle points in a single row matrix are those with the maximum value"

exercises/practice/saddle-points/saddle-points.coffee

@@ -0,0 +1,3 @@
+SaddlePoints = (matrix) ->
+
+module.exports = SaddlePoints

exercises/practice/saddle-points/saddle-points.spec.coffee

@@ -0,0 +1,76 @@
+SaddlePoints = require './saddle-points'
+
+describe 'SaddlePoints', ->
+  it 'can identify single saddle point', ->
+    matrix = [
+      [9, 8, 7]
+      [5, 3, 2]
+      [6, 6, 7]]  
+    results = SaddlePoints matrix
+    expect(results.sort()).toEqual [{row: 2, column: 1}]
+
+  xit 'can identify that empty matrix has no saddle points', ->
+    matrix = [[]]
+    results = SaddlePoints matrix
+    expect(results.sort()).toEqual []
+
+  xit 'can identify lack of saddle points when there are none', ->
+    matrix = [
+      [1, 2, 3]
+      [3, 1, 2]
+      [2, 3, 1]]
+    results = SaddlePoints matrix
+    expect(results.sort()).toEqual []
+
+  xit 'can identify multiple saddle points in a column', ->
+    matrix = [
+      [4, 5, 4]
+      [3, 5, 5]
+      [1, 5, 4]]
+    results = SaddlePoints matrix
+    expect(results.sort()).toEqual [{row: 1, column: 2}
+                                    {row: 2, column: 2}
+                                    {row: 3, column: 2}]
+
+  xit 'can identify multiple saddle points in a row', ->
+    matrix = [
+      [6, 7, 8]
+      [5, 5, 5]
+      [7, 5, 6]]
+    results = SaddlePoints matrix
+    expect(results.sort()).toEqual [{row: 2, column: 1}
+                                    {row: 2, column: 2}
+                                    {row: 2, column: 3}]
+
+  xit 'can identify saddle point in bottom right corner', ->
+    matrix = [
+      [8, 7, 9]
+      [6, 7, 6]
+      [3, 2, 5]]
+    results = SaddlePoints matrix
+    expect(results.sort()).toEqual [{row: 3, column: 3}]
+
+  xit 'can identify saddle points in a non square matrix', ->
+    matrix = [
+      [3, 1, 3]
+      [3, 2, 4]]
+    results = SaddlePoints matrix
+    expect(results.sort()).toEqual [{row: 1, column: 1}
+                                    {row: 1, column: 3}]
+
+  xit 'can identify that saddle points in a single column matrix are those with the minimum value', ->
+    matrix = [
+      [2]
+      [1]
+      [4]
+      [1]]
+    results = SaddlePoints matrix
+    expect(results.sort()).toEqual [{row: 2, column: 1}
+                                    {row: 4, column: 1}] 
+
+  xit 'can identify that saddle points in a single row matrix are those with the maximum value', ->
+    matrix = [[2, 5, 3, 5]]
+    results = SaddlePoints matrix
+    expect(results.sort()).toEqual [{row: 1, column: 2}
+                                    {row: 1, column: 4}]
+