水池问题的lua语言算法（面试题分析：我的Twitter技术面试失败了）

twitter面试题内容

“看下面这个图片”

“在这个图片里我们有不同高度的墙。这个图片由一个整数数组所代表，数组中每个数是墙的高度。上边的图可以表示为数组[2,5,1,2,3,4,7,7,6]”

“假如开始下雨了，那么墙之间的水坑能够装多少水呢？”

闲来无事给出一份解决此问题的lua代码（https://gist.github.com/jianchenglee/7262518）：

-- author ljc

-- 1) find the max value, split the array to 2 array

-- 2) compute the increment ,get 2 increment array

-- 3) get the result by the increment value(if there are a minus value,then retain water,until one by one accumulation value become plus,then go on next)

waterpool={2,4,3,5,1,2,3,2,3,7,7,6,7,6,4,5}

testcase_1 = {2,5,1,2,3,4,7,7,6}

testcase_2 = {2,5,1,3,1,2,1,7,7,6}

testcase_3 = {6,1,4,6,7,5,1,6,4}

function watertotal(o)

-- v1:tempvalue total: result value


-- v_max,i_max: the biggest value and the index of the input array


-- waterpool_q1: first half increment value array waterpool_q2: secopd half increment value array


local v1,v_max,i_max,total=0,0,0,0,0;


local waterpool_q1={};


local waterpool_q2={};

local allnumber=table.maxn(o)

--1)


for i,v in ipairs(o) do


if v>v_max then


v_max=v


i_max=i


end


end

--2)


-- generate waterpool_q1


for i=1,i_max-1,1 do


--print(o[i]-v1)


table.insert(waterpool_q1,o[i]-v1)


v1=o[i]


end

-- generate waterpool_q2


v1=0


for i=allnumber,i_max,-1 do


--print(o[i]-v1)


table.insert(waterpool_q2,o[i]-v1)


v1=o[i]

end

--3)


-- the result of waterpool_q1


v1=0

for i,v in ipairs(waterpool_q1) do

if v<0 and v1>=0 then


v1=v


total=total+math.abs(v1)


elseif (v1+v<0) then


v1=v1+v


total=total+math.abs(v1)


elseif v+v1>=0 then


v1=0

end


--print(math.abs(v1))


end

-- the result of waterpool_q1


v1=0


for i,v in ipairs(waterpool_q2) do

if v<0 and v1>=0 then


v1=v


total=total+math.abs(v1)


elseif (v1+v<0) then


v1=v1+v


total=total+math.abs(v1)


elseif v+v1>=0 then


v1=0

end


--print(math.abs(v1))


end

print(total)

end

-- test the function

watertotal(waterpool)

watertotal(testcase_1)

watertotal(testcase_2)

watertotal(testcase_3)

测试结果：

>lua -e "io.stdout:setvbuf 'no'" "waterpool.lua" 
17
10
17
13