Add solution for Challenge 19 (#724)

Co-authored-by: go-interview-practice-bot[bot] <230190823+go-interview-practice-bot[bot]@users.noreply.github.com>

Author: Johrespi

challenge-19/submissions/Johrespi/solution-template.go

@@ -0,0 +1,105 @@
+package main
+
+import (
+	"fmt"
+)
+
+func main() {
+	// Example slice for testing
+	numbers := []int{3, 1, 4, 1, 5, 9, 2, 6}
+
+	// Test FindMax
+	max := FindMax(numbers)
+	fmt.Printf("Maximum value: %d\n", max)
+
+	// Test RemoveDuplicates
+	unique := RemoveDuplicates(numbers)
+	fmt.Printf("After removing duplicates: %v\n", unique)
+
+	// Test ReverseSlice
+	reversed := ReverseSlice(numbers)
+	fmt.Printf("Reversed: %v\n", reversed)
+
+	// Test FilterEven
+	evenOnly := FilterEven(numbers)
+	fmt.Printf("Even numbers only: %v\n", evenOnly)
+}
+
+// FindMax returns the maximum value in a slice of integers.
+// If the slice is empty, it returns 0.
+func FindMax(numbers []int) int {
+	// TODO: Implement this function
+	if len(numbers) == 0 {
+	    return 0
+	}
+	
+    max := numbers[0]
+	
+	for i := 1; i < len(numbers); i++ {
+	    if numbers[i] > max {
+	        max = numbers[i]
+	    }
+	}
+	
+	return max
+}
+
+// RemoveDuplicates returns a new slice with duplicate values removed,
+// preserving the original order of elements.
+func RemoveDuplicates(numbers []int) []int {
+	// TODO: Implement this function
+	
+	if len(numbers) == 0 {
+	    return []int{}
+	}
+	
+	var res []int
+	m := make(map[int]struct{})
+	
+	for _, e := range numbers {
+	    _, exists := m[e]
+	    if !exists{
+	        m[e] = struct{}{}
+	        res = append(res, e)
+	    }
+	}
+	return res
+}
+
+// ReverseSlice returns a new slice with elements in reverse order.
+func ReverseSlice(slice []int) []int {
+	// TODO: Implement this function
+	
+	if len(slice) == 0 {
+	    return []int{}
+	}
+	
+	var res []int
+	
+	for i := len(slice) -1; i >= 0; i--{
+	    res = append(res, slice[i])
+	}
+	return res
+}
+
+// FilterEven returns a new slice containing only the even numbers
+// from the original slice.
+func FilterEven(numbers []int) []int {
+	// TODO: Implement this function
+	if len(numbers) == 0 {
+	    return []int{}
+	}
+	
+	var res []int
+	for _, e := range numbers {
+	    if e % 2 == 0 {
+	        res = append(res, e)
+	    }
+	}
+	
+	if len(res) == 0 {
+	    return []int{}
+	}
+	
+	return res
+}