@above...can you please enlighten me about the second term in the dp expression And are you sure its O(n) ?
On Fri, Jan 28, 2011 at 7:08 PM, sankalp srivastava < [email protected]> wrote: > This can be done in O(n) very easily , similar to Longest increasing > subsequence > > Solution :- > > dp[l]= maximum length of the zigzag sequence upto the length l > > //At any position , the particular number in the array can either > extend the zigzag sequence containing the last element or it can start > one of it's own . So the recurrance becomes > > dp[i]= max(dp[j]) ,and diff[A[p[j]]]^(A[i]-A[p[j]]&31)!=0 , j<i > > find out the maximum in this array , it will get you the answer . > > PS:- You can also check out the Topcoder tutorials . > > On Jan 27, 7:41 pm, bittu <[email protected]> wrote: > > well I found it as it Can be Done in O(n). but with additional space > > O(n) > > here program is written in Java > > > > public class ZigZag > > { > > > > public int longestZigZag(int[] sequence) > > { > > if (sequence.length==1) return 1; > > if (sequence.length==2) return 2; > > int[] diff = new int[sequence.length-1]; > > > > for (int i=1;i<sequence.length;i++) > > { > > diff[i-1]=sequence[i]-sequence[i-1]; > > } > > > > //90% Program is done here it self. by looking at the sign if > > alternative number in auxiliary array we can count longest zigzag > > array > > > > int sign=sign(diff[0]); > > int count=0; > > if (sign!=0) > > count=1; > > > > for (int i=1;i<diff.length;i++) > > { > > int nextsign=sign(diff[i]); > > if (sign*nextsign==-1){ > > sign=nextsign; > > count++; > > } > > } > > return count+1; > > } > > > > public int sign(int a) > > { > > if (a==0) return 0; > > return a/Math.abs(a); > > } > > > > public static void main(String[] args) > > { > > ZigZag z = new ZigZag(); > > System.out.println(z.longestZigZag(new int[] { 1, 7, 4, 9, 2, 5 })); > > System.out.println(z.longestZigZag(new int[] { 1, 17, 5, 10, 13, 15, > > 10, 5, 16, 8 })); > > > > } > > > > } > > > > Try for Inplace > > > > Thanks & Regards > > Shashank Mani ""The best way to escape from a problem is to solve it." > > -- > You received this message because you are subscribed to the Google Groups > "Algorithm Geeks" group. > To post to this group, send email to [email protected]. > To unsubscribe from this group, send email to > [email protected]<algogeeks%[email protected]> > . > For more options, visit this group at > http://groups.google.com/group/algogeeks?hl=en. > > -- S.Nishaanth, Computer Science and engineering, IIT Madras. -- You received this message because you are subscribed to the Google Groups "Algorithm Geeks" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/algogeeks?hl=en.
