// this package is mostly copy-pasted from golang's std container/heap
// I changed Interface, Pop and Push in order to get rid of type assertions
// usage can be found in test file, benchmarks show that we can get about 27% of speedup for 1000 elems, or 10% for 10M elems (tested on go1.4)
package gheap

type Interface interface {
	Len() int
	Less(i, j int) bool
	Swap(i, j int)
}

func Init(h Interface) {
	// heapify
	n := h.Len()
	for i := n/2 - 1; i >= 0; i-- {
		down(h, i, n)
	}
}

// put new element at Len() position before calling Push(h)
// you must also increase Len
func Push(h Interface) {
	up(h, h.Len()-1)
}

// after calling Pop() top element will be at position Len()-1
// you must decrease Len after this call
func Pop(h Interface) {
	n := h.Len() - 1
	h.Swap(0, n)
	down(h, 0, n)
}

func up(h Interface, j int) {
	for {
		i := (j - 1) / 2 // parent
		if i == j || !h.Less(j, i) {
			break
		}
		h.Swap(i, j)
		j = i
	}
}

func down(h Interface, i, n int) {
	for {
		j1 := 2*i + 1
		if j1 >= n || j1 < 0 { // j1 < 0 after int overflow
			break
		}
		j := j1 // left child
		if j2 := j1 + 1; j2 < n && !h.Less(j1, j2) {
			j = j2 // = 2*i + 2  // right child
		}
		if !h.Less(j, i) {
			break
		}
		h.Swap(i, j)
		i = j
	}
}