Calculate the number of K nearest to the median in an unordered array in the O (n) time.

Asked yesterday, so I immediately thought of a method.

The problem is that given an unordered array, finding the nearest K number to the median requires O (n) complexity.

The idea is as follows:

First, we need to know that the median of unordered Arrays can be obtained within the O (n) time by using linear time selection.

(1) O (n) calculates the median of unordered arrays.

(2) subtract the median from all the numbers in the array and take the absolute value to get a new array. Each number in this array represents its distance from the median. Complexity O (n ).

(3) using the linear time selection method, we can obtain the number of K at O (n) time. At this time, all the numbers on the left of K are smaller than K, and K is the smallest number.

(4) The original number corresponding to the minimum K number is the k Number closest to the median.

This completes the requirements.