2.6 ORDER STATISTICS A problem closely related to sorting is that of selecting the kth smallest ele- ment in a sequence of n elements.† One obvious solution is to sort the sequence into nondecreasing order and then locate the kth element. As we have seen, this would require n log n comparisons. By a careful application of the divide-and-conquer strategy, we can find the kth smallest element in O(n) steps. An important special case occurs when k = [n/2], in which case we are finding the median of a sequence in linear time. Algorithm 3.6. Finding the kth smallest element. Input. A sequence S of n elements drawn from a linearly ordered set and an integer k, 1 ≤ k ≤ n. Output. The kth smallest element in S. Method. We use the recursive procedure SELECT in Fig. 3.10. ☐ Let us examine Algorithm 3.6 intuitively to see why it works. The basic idea is to partition the given sequence about some element m into three subsequences S₁, S., S₁ such that S, contains all elements less than m, S, all Strictly speaking, the kth smallest of a sequence a₁. da, is an element b in the sequence such that there are at most k - 1 values for i for which a,
2.6 ORDER STATISTICS A problem closely related to sorting is that of selecting the kth smallest ele- ment in a sequence of n elements.† One obvious solution is to sort the sequence into nondecreasing order and then locate the kth element. As we have seen, this would require n log n comparisons. By a careful application of the divide-and-conquer strategy, we can find the kth smallest element in O(n) steps. An important special case occurs when k = [n/2], in which case we are finding the median of a sequence in linear time. Algorithm 3.6. Finding the kth smallest element. Input. A sequence S of n elements drawn from a linearly ordered set and an integer k, 1 ≤ k ≤ n. Output. The kth smallest element in S. Method. We use the recursive procedure SELECT in Fig. 3.10. ☐ Let us examine Algorithm 3.6 intuitively to see why it works. The basic idea is to partition the given sequence about some element m into three subsequences S₁, S., S₁ such that S, contains all elements less than m, S, all Strictly speaking, the kth smallest of a sequence a₁. da, is an element b in the sequence such that there are at most k - 1 values for i for which a,
Database System Concepts
7th Edition
ISBN:9780078022159
Author:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
Publisher:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
Chapter1: Introduction
Section: Chapter Questions
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