golang - max heap without using heap package

package main

import (
	"fmt"
	"encoding/json"
)

func maxHeap (input []int) {
	l := len(input)
	
	for i := l/2 - 1; i>=0; i-- {
		heapify(input, i, l)
	}
} 

func heapify (input []int, i int, n int) {
	largest := i
	l := 2 * i + 1
	r := 2 * i + 2
	
	if l < n && input[l] > input[i] {
		largest = l
	}
	
	if r < n && input[r] > input[largest] {
		largest = r
	}
	
	if i != largest {
		// swap them
		temp := input[largest]
		input[largest] = input[i]
		input[i] = temp
		
		// heapify the changed child tree
		heapify(input, largest, n)
	}
}

func main() {
	input := []int{0, 4, 10, 3 ,5, 1, 3, 11, 6, 12, 7}
	
	maxHeap(input)
}