We have a collection of rocks, each rock has a positive integer weight.
Each turn, we choose the two heaviest rocks and smash them together. Suppose the stones have weights x and y with x <= y. The result of this smash is:
<li>If <code>x == y</code>, both stones are totally destroyed;</li>
<li>If <code>x != y</code>, the stone of weight <code>x</code> is totally destroyed, and the stone of weight <code>y</code> has new weight <code>y-x</code>.</li>
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.
Note:
<li><code>1 <= stones.length <= 30</code></li>
<li><code>1 <= stones[i] <= 1000</code></li>