Reduce array length

Am trying to merge two string array to one. The resulting array should have all duplicates element removed.

func MergeArrays(str1, str2 []string) []string {
	c := make([]string, len(str1)+len(str2), cap(str1)+cap(str2))
	k := make(map[string]bool)
	for i, s := range str1 {
		if _, ok := k
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; !ok {
			c[i] = s
			k
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 = true
		}
	}
	for j, s := range str2 {
		if _, ok := k
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; !ok {
			c[j+len(str1)] = s
			k
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 = true
		}
	}
	return c
}

Test Data

str1 := []string{"a", "b"}
str2 := []string{"c", "d", "a"}

Output:
"a", "b", "c", "d"
length of the array "5"

Am getting the output i want, but the length of the array should be 4 and not 5. I can understand why it prints 5, but i want the output array of length 4.
Is there other way to merge two arrays.

They're slices, not arrays and here's an example that solves your use-case:

package main

import "fmt"

func MergeStringSlices(str1, str2 []string) []string {
	m := make([]string, len(str1), len(str1)+len(str2))
	copy(m, str1)
already_seen:
	for _, s := range str2 {
		for _, t := range m {
			if s == t {
				continue already_seen
			}
		}
		m = append(m, s)
	}
	return m
}

func main() {
	str1 := []string{"a", "b"}
	str2 := []string{"c", "d", "a"}
	fmt.Printf("%#v\n", MergeStringSlices(str1, str2))
}

Start with a length of zero and add one when you append an element. For example,

package main

import "fmt"

func MergeArrays(a1, a2 []string) []string {
	m := make([]string, 0, len(a1)+len(a2))
	k := make(map[string]bool, len(a1)+len(a2))
	for _, aa := range [][]string{a1, a2} {
		for _, s := range aa {
			if !k
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 {
				m = append(m, s)
				k
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 = true
			}
		}
	}
	return m
}

func main() {
	a1 := []string{"a", "b"}
	a2 := []string{"c", "d", "a"}
	m := MergeArrays(a1, a2)
	fmt.Println(len(m), m)
}

Output:

4 [a b c d]