Monday, March 21, 2016

DropBox Interview Misc


http://www.1point3acres.com/bbs/thread-177627-1-1.html
/* 2-d array of "sharpness" values. Fine the path from left to right which has the highest minimum sharpness. 路径必须是从左往右,先有个起始点,然后每次要往右上,正右或右下跳一步。也就是说,路径长度是列数n,假设路径为(i1,1),(i2,2),...,(in,n),路径必须满足每对i_k与i_{k-1}的距离不能大于1.
. from: 1point3acres.com/bbs 
.5 .7 .2
.7 .5 .8
.9 .1 .5-google 1point3acres
. 鍥磋鎴戜滑@1point 3 acres
在这个例子中,理想路径是.7->.7->.8因为这条路径中的最小值.7在所有路径中最大。只需要返回这个值,不需要返回路径。这是道dp问题

follow up:
如果图片是1million*1million的怎么办,整张图片读不进内存,我答说dp结构可以改成一维的,然后每次只读一列。小哥说每次读一列的第一个字符非常耗时,因为要不断的跳读指针,然后我说可以对这个矩阵转置写到另外一个文件里,然后每次想做这个函数就对这个新文件操作就好了,这样就能按行读。小哥就问我怎么转置再存到另外一个文件里,我说根据内存大小可以多读几列。然后小哥就说还可以再优化,他说这有一个balance,读行输出列,写文件就很耗时,读列输出行,读文件就很耗时(主要问题是 写指针或读指针跳转到下一行 所带来的时间消耗),其实听到这里我就应该有反应了,但当时还是傻傻的想。最后结果是每次根据内存大小读一个接近正方形的矩形,将他们写到新文件,再读下一块矩形。这样的话,读写指针跳转次数就最小了。
http://www.1point3acres.com/bbs/thread-180491-1-1.html
code是他家的duplicate file,一开始我尝试边写代码边说话,他不理我,楼主口语渣,也说不下去,结果后半段完全就是闷头写代码
我在read file时用的bfs,出了点小问题,在work through的时候修改,可能是扣分点
问了我复杂度,md5不能证明两个file一样,我后来说可以再作为filter,比较byte array才行
问我如果file很大怎么办,因为我读file的时候就是1kb的size读取,我回答说所有相同md5的file再拿出来一个一个比较
问我这个1kb的读取是从头好还是从尾好,我说从头好,但是说不出为什么,一开始说从头读速度快,他说从哪里读速度都一样,然后他给我解释了,然而我并没听明白他的英语。。
http://www.1point3acres.com/bbs/thread-170171-1-1.html
设计两个function,分别是log_hit()和get_hit_number_in_last_5_mins(). 之前在面经上也见过这题,就是要记录一个web被visited的次数以及返回过去5 min内被visited的次数
http://www.1point3acres.com/bbs/thread-180309-1-1.html

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