find the kth largest key in a map in go

main.go
import (
	"container/heap"
	"sort"
)

// Approach 1: sort and return kth element
func findKthLargestKeyBySorting(m map[int]string, k int) int {
	if k <= 0 || k > len(m) {
		return 0 // invalid k value
	}
	keys := make([]int, 0, len(m))
	for k := range m {
		keys = append(keys, k)
	}
	sort.Sort(sort.Reverse(sort.IntSlice(keys)))
	return keys[k-1]
}

// Approach 2: use max heap and remove top k elements
func findKthLargestKeyByHeap(m map[int]string, k int) int {
	if k <= 0 || k > len(m) {
		return 0 // invalid k value
	}
	keys := make([]int, 0, len(m))
	for k := range m {
		keys = append(keys, k)
	}
	h := IntMaxHeap(keys)
	heap.Init(&h)
	for i := 1; i < k; i++ {
		heap.Pop(&h)
	}
	return heap.Pop(&h).(int)
}

// IntMaxHeap defines a max heap of int keys
type IntMaxHeap []int

func (h IntMaxHeap) Len() int           { return len(h) }
func (h IntMaxHeap) Less(i, j int) bool { return h[i] > h[j] }
func (h IntMaxHeap) Swap(i, j int)      { h[i], h[j] = h[j], h[i] }

func (h *IntMaxHeap) Push(x interface{}) {
	*h = append(*h, x.(int))
}

func (h *IntMaxHeap) Pop() interface{} {
	old := *h
	n := len(old)
	x := old[n-1]
	*h = old[0 : n-1]
	return x
}
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