Results 1 to 9 of 9
 06282012, 03:15 PM #1Member
 Join Date
 Jun 2012
 Posts
 6
 Rep Power
 0
A magnitude pole of an array problem
Hello all;
The problem is to find the magnitude pole of an array:
"A magnitude pole of an array A consisting of N integers is an index K such that all elements with smaller indexes have values lower or equal to A[K] and all elements with greater indexes have values greater or equal to A[K], i.e.
For example:
5 is a magnitude pole of array A such that
A[0]=4, A[1]=2, A[2]=2, A[3]=3, A[4]=1, A[5]=4, A[6]=7, A[7]=8, A[8]=6, A[9]=9."
I need to figure out why this solution does not work:
Java Code:public int magnitudePole(int[] A) { boolean foundLeft = true; boolean foundRight = true; for(int i = 0; i < A.length; i++) { for(int j = i  1; j >= 0; j) { if((A[i]  A[j]) < 0 ) { foundLeft = false; break; } else { foundLeft = true; } } for(int j = i + 1; j < A.length && foundLeft; j++) { if((A[j]  A[i]) < 0) { foundRight = false; break; } } if(foundLeft && foundRight) { return i; } } return 1; }
Thank you for your help.
 06282012, 03:24 PM #2
Re: A magnitude pole of an array problem
How doesn't it work? What do you expect it to do? What does it do instead? You need to step through this with a debugger, or at the very least add some print statements, until you understand exactly what the program is doing.
How to Ask Questions the Smart Way
Static Void Games  Play indie games, learn from game tutorials and source code, upload your own games!
 06282012, 03:37 PM #3Member
 Join Date
 Jun 2012
 Posts
 6
 Rep Power
 0
Re: A magnitude pole of an array problem
Thank you for your help. With this example :
A[0]=4, A[1]=2, A[2]=2, A[3]=3, A[4]=1, A[5]=4, A[6]=7, A[7]=8, A[8]=6, A[9]=9."
It should give 5 , but it gives 1.
I went through every element on paper and it must work, I printed some values , but it does not help much.
Any help?
 06282012, 05:13 PM #4
Re: A magnitude pole of an array problem
Like I said, you'll have to step through this with a debugger, or at least add more print statements, until you figure out what's going on.
How to Ask Questions the Smart Way
Static Void Games  Play indie games, learn from game tutorials and source code, upload your own games!
 06282012, 06:18 PM #5
Re: A magnitude pole of an array problem
It would help us to understand what the code is trying to do if you added comments to it describing what each part of the code is doing.
If you don't understand my response, don't ignore it, ask a question.
 06292012, 07:47 AM #6Banned
 Join Date
 Jun 2012
 Location
 Beijing,China
 Posts
 34
 Rep Power
 0
Re: A magnitude pole of an array problem
Your code looks good.But you need to check it more ,especial for your logic.
Java Code:public class x{ public static void main(String [] args) { int[] A={4,2,2,3,1,4,7,8,6,9}; boolean foundLeft ; boolean foundRight ; boolean found=false; for(int i=1;i< A.length1;i++) { foundLeft = true; foundRight = true; for(int j=0;j<i;j++){ if (A[j] > A[i]) foundLeft=false; } for(int k=i+1;k<A.length;k++){ if (A[i] > A[k]) foundRight=false; } if (foundLeft && foundRight) {System.out.println("Found it: " + i);found=true;} } if ( ! found ) System.out.println("Not Found."); } }
Ksharp
 06292012, 07:56 AM #7Member
 Join Date
 Jun 2012
 Posts
 6
 Rep Power
 0
Re: A magnitude pole of an array problem
Well I used your two advices printing statements, and checking every part. The problem in the code was, it should reset foundRight to true in the end of the main loop. So the code after the correction:
Java Code:public int magnitudePole(int[] A) { boolean foundLeft = true; boolean foundRight = true; //loop over each element and break the loop when you find the correct answer for(int i = 0; i < A.length; i++) { //check all the left elements of the current element for(int j = i  1; j >= 0; j) { if((A[i]  A[j]) < 0 ) { foundLeft = false; break; } else { foundLeft = true; } } //if the all the left elements less than the current one check all the right elements of the current element for(int j = i + 1; j < A.length && foundLeft; j++) { if((A[j]  A[i]) < 0) { foundRight = false; break; } } //if all the left elements less than the current element //and if all the right elements bigger than the current element // return the index of the current element if(foundLeft && foundRight) { return i; } //the killing mistake was foundRight should be reset to true //and this was what made the code give the wrong answer even though the method is correct foundRight = true; } return 1; }
Ok! thank you guys for your help.
Done!
 04212013, 11:07 AM #8Rahul Shukla
 Join Date
 Apr 2013
 Location
 Pune India
 Posts
 1
 Rep Power
 0
Re: A magnitude pole of an array problem Solution with O(n) time complexity
public int magnitudePole2(int[] A) {
int[] max = new int[A.length];
int[] min = new int[A.length];
int mx = Integer.MIN_VALUE;
int mn = Integer.MAX_VALUE;
for (int i = 0; i < A.length; i++) {
if (A[i] > mx)
mx = A[i];
max[i] = mx;
}
min[A.length  1] = mn;
for (int i = A.length  1; i > 0; i) {
if (A[i] < mn)
mn = A[i];
min[i  1] = mn;
}
for (int i = 0; i < A.length; i++) {
if (A[i] >= max[i] && A[i] < min[i])
return i;
}
return 1;
}
 04212013, 12:00 PM #9
 Join Date
 Sep 2008
 Location
 Voorschoten, the Netherlands
 Posts
 13,352
 Blog Entries
 7
 Rep Power
 20
Similar Threads

A problem with using an array
By Czuks in forum New To JavaReplies: 5Last Post: 12212011, 05:11 PM 
Display Array on another class after extracting from txt file and into array problem
By jonathan920 in forum NetBeansReplies: 0Last Post: 05122011, 07:04 PM 
Array Problem
By Aiquoc in forum New To JavaReplies: 6Last Post: 03292011, 04:03 AM 
array problem
By aizen92 in forum New To JavaReplies: 26Last Post: 12212010, 05:42 AM 
array problem
By jabo in forum New To JavaReplies: 2Last Post: 03312010, 09:54 AM
Bookmarks