推箱子


推箱子
5. 一个洞穴里面很多格,每一格都是不同的高度,还有一堆object, 每个的高度不同,问这个洞穴最多可以放多少个object,往洞穴放object的话要注意是从洞口往里放,所以靠近洞口的格子的高度会限制后面的高度,因为object会被卡住。。. 每个格子只能放一个object,object不能叠加。


第三题:地里的面经题。有一个山洞,可以看作一维height数组。  另外有一堆箱子boxes, 要求将箱子从外面推到山洞里面,问最多能推多少箱子进山洞。楼主先解释了为什么要先将箱子高度排序,先推矮箱子,再推高箱子。同时山洞的每一个位置i都最多能容许min(heights[:i])的箱子通过。 根据这点建立一个allowedHeight数组,可以看出是单调不增的序列, 因此对每个箱子高度可以bisect寻找allowedHeight里面对应的position index.  讨论了时间复杂度 O(log(len(height))*len(boxes))。电脑写了code后和面试小哥讨论了几点可以优化的地方,最后小哥表示时间复杂度还可以优化,在提示下使用two pointer方法,让两个pointer分别指向最矮箱子的position和最小allowedHeight position, 依次比较二者的大小来分别递增两pointer。 时间复杂度可以变成O(len(height)+len(boxes))


我来描述一下吧:

假设山洞有三个格子,从左到右(也是从最深到洞口的顺序)的高度分别是: 5, 10, 6 【洞口】。见下图:

[Bash shell] 纯文本查看 复制代码
?
       ------
      |      |------
|-----|     
|
|____________________ 洞口
 
 高度5  高度10  高度6



那么可知最左的格子最多只能放5,中间的格子只能放6,因为6以上的箱子无法从洞口通过最右边的只有高度6的格子,也就不可能到中间。最右边的格子最多只能放6。因此箱子进洞有着单调性。另外格子里最多可以放一个箱子。

如果我有这些箱子:📦 10, 30, 6, 5, 8,7,那么在排序以后,我 应该 5 放最左,6放中间或者左边。有一个格子空着。7,8,10,30这些箱子不能放入。

https://www.1point3acres.com/bbs ... read&tid=511673

https://www.1point3acres.com/bbs ... read&tid=444025


洞O[n] 做递减数组
箱子排序, 挨个match.



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