ps1num1c

ps1num1c - then for n = k the algorithm will attempt to...

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1(c). Input: Give the applicant set {A1, A2, …, An} and the job set {J1, J2, …, Jn} such that every applicant and every job ranks the other in exactly the reverse order. E.g. each applicant has preference in the order of {Jn, Jn-1, …, J1} and each job has preference in the order of {An, An-1, …, A1}. Complexity : The above input will cause the program to run in O (n!) which is exponential. Base case: if we’re given that n = 1, then there’s exactly one matching between J1 and A1, which is stable by default. So one operation is performed which is exponential in 1. Note : at every step within the subproblem of k<n, if Ak – Jn are not matched, the marriage is unstable because each whoever Ak is matched with will be higher on his preference list than Jn and vice versa for Jn to Ak. Assume that for some n=k-1, the running time for the function of our inputs A and J is O((n-1)!),
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Unformatted text preview: then for n = k, the algorithm will attempt to make matches until the An-Jn match is made, at which time the marriage will finally become stable. Since each iteration within the for loop removes Jn and Ai to be matched up later, the recursive call will be made on an applicant set A’ and a job set J’ of cardinality k-1 and of which every element of each set have a list of preference into the other set in the exact opposite order, which can be exchanged exactly as the input for the subproblem of n=k-1, which from the induction hypothesis takes O ((n-1)!) time to solve. However, since we can guarantee that no set of marriages are stable until the An-Jn match is made, which doesn’t happen until after the for loop iterates for n steps, we will have to solve the same subproblem of order O((n-1)!) n times, making for O(n!) complexity....
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This note was uploaded on 03/12/2012 for the course CS 4820 taught by Professor Kleinberg during the Spring '08 term at Cornell.

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