Add task5 in php

Author: Holger Lösken

README.md

@@ -44,7 +44,7 @@ Write a function `jump_out_of_array` that outputs
 * the amount of jumps until you jump out of the array
 * `-1` when you reach the end of the array but do not jump out
 
-** Requirements:**
+**Requirements:**
 * Array size is indefinite
 * Array elements are integers, positive and negative
 
@@ -54,12 +54,35 @@ Given an array of `A[2, 3, -1, 1, 6, 4]`.
 
 ![](./docs/t4/task4.png)
 
-* Jump 1: A[0] + 2 = A[2]
-* Jump 2: A[2] + (-1) = A[1]
-* Jump 3: A[1] + 3 = A[4]
-* Jump 4: A[4] + 6 = out of range
+* Jump 1: `A[0]` + `2` = `A[2]`
+* Jump 2: `A[2]` + `(-1)` = `A[1]`
+* Jump 3: `A[1]` + `3` = `A[4]`
+* Jump 4: `A[4]` + `6` = out of range
+
+So the result is `4`, you need `4` jumps to jump out of the array.
+
+### Task 5
+
+Find the k-complement pairs in an array of a given number. Write a function `k_complement` that that outputs the amount
+of pairs.
+
+**Requirements:**
+
+_Do not_ use nested loops to solve this problem, because of a time complexity of the loop solution.
+[Check this thread](https://stackoverflow.com/questions/11032015/how-to-find-time-complexity-of-an-algorithm) to see what time complexity of an algorithm means.
+
+
+**Example:**
+
+Given a number `6` and an array `A[1, 8, -3, 0, 1, 3, -2, 4, 5]` the amount of pairs is `7`.
 
-So the result is `4`, you need 4 jumps to jump out of the array.
+* `A[0]` + `A[8]` = `1` + `5` = `6`
+* `A[1]` + `A[6]` = `8` + `-2` = `6`
+* `A[4]` + `A[8]` = `1` + `5` = `6`
+* `A[5]` + `A[5]` = `3` + `3` = `6`
+* `A[5]` + `A[5]` = `3` + `3` = `6`
+* `A[6]` + `A[1]` = `-2` + `8` = `6`
+* `A[8]` + `A[0]` = `5` + `1` = `6`
 
 ## Contribute
 

src/php/composer.json

@@ -10,7 +10,8 @@
             "t1/s1.php",
             "t2/s1.php",
             "t3/s1.php",
-            "t4/s1.php"
+            "t4/s1.php",
+            "t5/s1.php"
         ],
         "psr-4": {
             "Tests\\": "tests/"

src/php/t5/s1.php

@@ -0,0 +1,43 @@
+<?php
+
+declare(strict_types=1);
+
+function k_complement(int $k, array $a): int {
+    $amountComplimentary = 0;
+
+    /**
+     * Hold amount of occurrence of a single number inside starting array '$a'
+     * Structure is:
+     *  [
+     *      [
+     *          key: number
+     *          value: amount occurrence in original array '$a'
+     *      ],
+     *      [
+     *          ...
+     *      ],
+     *  ]
+     */
+    $occurrencesNumbers = [];
+
+    foreach ($a as $number) {
+        if (!array_key_exists($number, $occurrencesNumbers)) {
+            $occurrencesNumbers[$number] = 1;
+        } else {
+            $occurrencesNumbers[$number]++;
+        }
+    }
+
+    $numbers = array_keys($occurrencesNumbers);
+
+    foreach ($numbers as $number) {
+        // Building the complementary pair by subtracting one number from the target result
+        // and checking if the result (other pair part) exists
+        $result = $k - $number;
+        if (in_array($result, $numbers)) {
+            $amountComplimentary += $occurrencesNumbers[$number] * $occurrencesNumbers[$result];
+        }
+    }
+
+    return $amountComplimentary;
+}

src/php/tests/T5Test.php

@@ -0,0 +1,20 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tests;
+
+use PHPUnit\Framework\TestCase;
+
+final class T5Test extends TestCase
+{
+    public function testKcomplementPositiveNumber(): void
+    {
+        $this->assertSame(7, k_complement(6, [1, 8, -3, 0, 1, 3, -2, 4, 5]));
+    }
+
+    public function testKcomplementNegativeNumber(): void
+    {
+        $this->assertSame(2, k_complement(-1, [-1, 2, 0]));
+    }
+}