Merge pull request #350 from sir-gon/feature/greedy_florist

[Hacker Rank] Interview Preparation Kit: Greedy Algorithms: Greedy Fl…

Author: sir-gon

docs/hackerrank/interview_preparation_kit/greedy_algorithms/greedy-florist-solution-notes.md

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+# [Greedy Algorithms: Greedy Florist](https://www.hackerrank.com/challenges/greedy-florist)
+
+- Difficulty:  `#medium`
+- Category: `#ProblemSolvingBasic` `#greedyalgorithms`
+
+## About the problem statement
+
+At first it seems a bit confusing. Due the problem statement tends to
+make us believe that the most convenient thing is to start with the highest
+numbers, but the examples doesn't not present a logical descending order.
+
+## Way of thinking
+
+After rereading the problem several times it can be determined that:
+
+- It does not matter who the buyers are, nor in what order they buy,
+nor how much each one buys.
+The important thing is how many people are organized
+into a group to minimize the purchase price.
+
+- If the number of people in the group is greater than or equal to
+the number of different flowers, then the price is the lowest possible,
+because they can all be purchased "in a single pass",
+making each person in the group (or less) buy 1 unit.
+
+- The price of flowers does matter, therefore it is more convenient to buy
+the most expensive ones first.
+Each "round" of purchasing makes the flowers more expensive,
+therefore it is better to buy the cheapest ones in the last "round."
+
+## Deductions
+
+- It seems convenient to sort the flower price list entry in descending order
+(or in ascending order, traversing the new sorted list in reverse).
+
+- The number of passes depends on how many "groups" of "k - people"
+fit in the list of flowers, that is:
+$ \textbf{\#(c) / k}$ (integer division)
+
+- At first I assumed that the order in which the traversal is done in
+the examples was a suggestion of the criteria in which the list of flowers
+should be traversed to reach the solution.
+
+    Finally, realizing that the price calculation in descending order
+    (and "the round" in which the purchase is made)
+    and the example were equivalent, made me consider the idea that the order of
+    the examples might just be a distractor,
+    introduced on purpose to make deducing the solution a little more difficult.

docs/hackerrank/interview_preparation_kit/greedy_algorithms/greedy-florist.md

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+# [Greedy Algorithms: Greedy Florist](https://www.hackerrank.com/challenges/greedy-florist)
+
+- Difficulty:  `#medium`
+- Category: `#ProblemSolvingBasic` `#greedyalgorithms`
+
+A group of friends want to buy a bouquet of flowers.
+The florist wants to maximize his number of new customers and the money he makes.
+To do this, he decides he'll multiply the price of each flower by the number
+of that customer's previously purchased flowers plus `1`.
+The first flower will be original price, $(0 + 1) \times \text{original price}$,
+the next will be $(1 + 1) \times \text{original price}$ and so on.
+
+Given the size of the group of friends, the number of flowers they want
+to purchase and the original prices of the flowers, determine the minimum cost
+to purchase all of the flowers.
+The number of flowers they want equals the length of the  array.
+
+## Example
+
+`c = [1, 2, 3, 4]`
+`k = 3`
+
+The length of `c = 4`, so they want to buy `4`  flowers total.
+Each will buy one of the flowers priced `[2, 3, 4]` at the original price.
+Having each purchased `x = 1` flower,
+the first flower in the list, `c[0]`, will now cost
+$ (
+    \textsf{\textbf{current purchase}}
+        +
+    \textsf{\textbf{previous purchase}}
+) \times
+\textsf{\textbf{c[0]}} $.
+The total cost is `2 + 3 + 4 + 2 = 11`.
+
+## Function Description
+
+Complete the getMinimumCost function in the editor below.
+
+getMinimumCost has the following parameter(s):
+
+- `int c[n]`: the original price of each flower
+- `int k`: the number of friends
+
+## Returns
+
+- `int`: the minimum cost to purchase all flowers
+
+## Input Format
+
+The first line contains two space-separated integers `n` and `k`,
+the number of flowers and the number of friends.
+The second line contains `n` space-separated positive integers `c[i]`,
+the original price of each flower.
+
+## Constraints
+
+- $ 1 \leq n, k \leq 100 $
+- $ 1 \leq c[i] \leq 10^5 $
+- $ answer < 2^31 $
+- $ 0 \leq i \leq n $
+
+## Sample Input 0
+
+```text
+3 3
+2 5 6
+```
+
+## Sample Output 0
+
+```text
+13
+```
+
+## Explanation 0
+
+There are `n = 3` flowers with costs `c = [2, 5, ,6]` and `k = 3` people in the group.
+If each person buys one flower,
+the total cost of prices paid is `2 + 5 + 6 = 13` dollars.
+Thus, we print `13` as our answer.
+
+## Sample Input 1
+
+```text
+3 2
+2 5 6
+```
+
+## Sample Output 1
+
+```text
+15
+```
+
+## Explanation 1
+
+There are `n = 3` flowers with costs `c = [2, 5, 6]` and `k = 2`
+people in the group.
+We can minimize the total purchase cost like so:
+
+1. The first person purchases 2 flowers in order of decreasing price;
+this means they buy the more expensive flower ($ c_1 = 5 $) first at price
+$
+    p_1 = (0 + 1) \times 5 = 5
+$
+dollars and the less expensive flower ($ c_0 = 5 $) second at price
+$
+    p_0 = (1 + 1) \times 2 = 4
+$
+ dollars.
+2. The second person buys the most expensive flower at price
+$
+    p_2 = (0 + 1) \times 6 = 6
+$
+dollars.
+
+We then print the sum of these purchases, which is `5 + 4 + 6 = 15`, as our answer.
+
+## Sample Input 2
+
+```text
+5 3
+1 3 5 7 9
+```
+
+## Sample Output 2
+
+```text
+29
+```
+
+## Explanation 2
+
+The friends buy flowers for `9, 7`,  and `3, 5`,  and `1` for a cost of
+`9 + 7 + 3 * (1 + 1) + 5 + 1 * (1 + 1) = 29`.

exercises/hackerrank/interview_preparation_kit/greedy_algorithms/greedy_florist.go

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+/**
+ * @link Problem definition [[docs/hackerrank/interview_preparation_kit/greedy_algorithms/greedy-florist.md]]
+ * @see Solution notes [[docs/hackerrank/interview_preparation_kit/greedy_algorithms/greedy-florist-solution-notes.md]]
+ */
+
+package hackerrank
+
+import (
+	"slices"
+)
+
+func getMinimumCost(k int32, c []int32) int32 {
+	// Sort the array
+	flowers := make([]int32, len(c))
+	copy(flowers, c)
+	slices.Sort(flowers)
+	slices.Reverse(flowers)
+
+	total := int32(0)
+	k_customers := int(k)
+
+	for i, flower_cost := range flowers {
+		var position = int32(i / k_customers)
+		total += int32(position+1) * int32(flower_cost)
+	}
+
+	return total
+}
+
+func GetMinimumCost(k int32, c []int32) int32 {
+	return getMinimumCost(k, c)
+}

exercises/hackerrank/interview_preparation_kit/greedy_algorithms/greedy_florist.testcases.json

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+[
+  {
+    "title": "Sample Test case 0",
+    "k": 3,
+    "c": [2, 5, 6],
+    "expected": 13
+  },
+  {
+    "title": "Sample Test case 1",
+    "k": 2,
+    "c": [2, 5, 6],
+    "expected": 15
+  },
+  {
+    "title": "Sample Test case 2",
+    "k": 3,
+    "c": [1, 3, 5, 7, 9],
+    "expected": 29
+  },
+  {
+    "title": "Test case 1",
+    "k": 3,
+    "c": [390225, 426456, 688267, 800389, 990107, 439248, 240638, 15991, 874479, 568754, 729927, 980985, 132244, 488186, 5037, 721765, 251885, 28458, 23710, 281490, 30935, 897665, 768945, 337228, 533277, 959855, 927447, 941485, 24242, 684459, 312855, 716170, 512600, 608266, 779912, 950103, 211756, 665028, 642996, 262173, 789020, 932421, 390745, 433434, 350262, 463568, 668809, 305781, 815771, 550800],
+    "expected": 163578911
+  }
+]

exercises/hackerrank/interview_preparation_kit/greedy_algorithms/greedy_florist_test.go

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+package hackerrank
+
+import (
+	"fmt"
+	"os"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"gon.cl/algorithms/utils"
+)
+
+type GreedyFloristTestCase struct {
+	C        []int32 `json:"c"`
+	K        int32   `json:"k"`
+	Expected int32   `json:"expected"`
+}
+
+var GreedyFloristTestCases []GreedyFloristTestCase
+
+// You can use testing.T, if you want to test the code without benchmarking
+func GreedyFloristSetupSuite(t testing.TB) {
+	wd, _ := os.Getwd()
+	filepath := wd + "/greedy_florist.testcases.json"
+	t.Log("Setup test cases from JSON: ", filepath)
+
+	var _, err = utils.LoadJSON(filepath, &GreedyFloristTestCases)
+	if err != nil {
+		t.Log(err)
+	}
+}
+
+func TestGreedyFlorist(t *testing.T) {
+
+	GreedyFloristSetupSuite(t)
+
+	for _, tt := range GreedyFloristTestCases {
+		testname := fmt.Sprintf("getMinimumCost(%v, %v) => %v \n", tt.K, tt.C, tt.Expected)
+		t.Run(testname, func(t *testing.T) {
+			ans := GetMinimumCost(tt.K, tt.C)
+			assert.Equal(t, tt.Expected, ans)
+		})
+	}
+}