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Posted on 2006-11-20
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Last Modified: 2010-03-31
Hi,

i have the following piece of code but cannot find out what
Pos
Ret
Temp

are asking for me to return can anyone give me any hints?

function LASTAT(s,num)
{       /* XImp  */
var pos in Int
var ret in Int
var temp in Stack of Int
temp <-- s
for (pos <-- 0 to 4)
{
  if (PEEK(temp) == num) then
    {  ret <-- pos  }
  temp <-- POP(temp)
}
return ret
}


Thanks
max
0
Comment
Question by:Max_AJApplegarth
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1 Comment
 
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Accepted Solution

by:
ADSLMark earned 2000 total points
ID: 17981925
It's not Java, but anyway.. it looks like the code takes 4 steps in a stack, comparing the num value with each value on the top of the stack each iteration.
Let's assume we denote a stack with the following notation:
[5, 3, 7, 1] where 5 is the top element.
Let's assume we look at the state at 3 different points namely:

function LASTAT(s,num)
{
    var pos in Int
    var ret in Int
    var temp in Stack of Int
    temp <-- s
>1>>>>>>>>>>>>>>>>>>>>>>>>
    for (pos <-- 0 to 4)
    {
        if (PEEK(temp) == num) then {  ret <-- pos  }
        temp <-- POP(temp)
>2>>>>>>>>>>>>>>>>>>>>>>>>
    }
>3>>>>>>>>>>>>>>>>>>>>>>>>
    return ret
}


Then in an example:
LASTAT([5, 3, 7, 1], 7);

[1] pos=0, ret=0, temp=[5,3,7,1], num=7
[2] pos=0, ret=0, temp=[3,7,1], num=7 (if statement compares PEEK(temp)=5 with num=7)
[2] pos=1, ret=0, temp=[7,1], num=7 (if statement compares PEEK(temp)=3 with num=7)
[2] pos=2, ret=2, temp=[1], num=7 (if statement compares PEEK(temp)=7 with num=7)
[2] pos=3, ret=2, temp=[], num=7 (if statement compares PEEK(temp)=1 with num=7)
[3] pos=3, ret=2, temp=[], num=7 (if statement compares PEEK(temp)=1 with num=7)

I just noticed that the name is LASTAT (=> LastAt). That's what it does, it finds the last index of num in a stack of 4 elements.

pos is used as counter through the stack
ret is used as return value
temp is used as stack copy (since there is a POP, the stack changes so a temporary value is necessary)

I made several assumptions about the language, but i guess this will be sufficient.

Mark
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