We have a collection of stones, each stone has a positive integer weight.

Each turn, we choose the two heaviest stones and smash them together.  Suppose the stones have weights x and y with x <= y.  The result of this smash is:

  • If x == y, both stones are totally destroyed;
  • If x != y, the stone of weight x is totally destroyed, and the stone of weight y has new weight y-x.

At the end, there is at most 1 stone left.  Return the weight of this stone (or 0 if there are no stones left.)

Example 1:

Input: [2,7,4,1,8,1]
Output: 1
Explanation: 
We combine 7 and 8 to get 1 so the array converts to [2,4,1,1,1] then,
we combine 2 and 4 to get 2 so the array converts to [2,1,1,1] then,
we combine 2 and 1 to get 1 so the array converts to [1,1,1] then,
we combine 1 and 1 to get 0 so the array converts to [1] then that's the value of last stone.
 

Solution:

import "container/heap"

type IntHeap []int

func (h IntHeap) Len() int {return len(h)}
func (h IntHeap) Less(x, y int) bool {return  h[x] > h[y]}
func (h IntHeap) Swap(x, y int) {h[x], h[y] = h[y], h[x]}
func (h *IntHeap) Push(x  interface{}) {
    *h = append(*h, x.(int))
}
func (h *IntHeap) Pop() interface{} {
    if len(*h) == 0 {
        return 0
    } 
    old := *h
    x := old[len(old) - 1]
    *h = old[0: len(old) - 1]
    return x
}

func lastStoneWeight(stones []int) int {
    h := &IntHeap{}
    heap.Init(h) //important
    for i := 0; i < len(stones); i++ {
        heap.Push(h, stones[i])
    }
    for len(*h) >= 2 {
        a := (heap.Pop(h)).(int)
        b := (heap.Pop(h)).(int)
        if b > a{
            b, a = a, b
        }
        heap.Push(h, a - b)
    }
    return (heap.Pop(h)).(int)
}