Below is my code for trying to understand the median of medians algorithm (using blocks of size 5). I understand how to get medians of the input, but I'm not sure how to code the block to keep recursing the input until I just have the median. Then after getting that median, I'm not sure how to use it as a pivot to throw away the useless information to partition the input. getMediansArray returns an array of size ceil(input.length/5) and getMedians just returns the median from an array (only used on arrays of length <= 5).
public static int[] findKthElement(int[] input, int k) {
int numOfMedians = (int) Math.ceil(input.length/5.0);
int[] medians = new int[numOfMedians];
medians = getMediansArray(input, medians)
// (1) This only gets the first iteration of medians of the
// input. How do I recurse on this until I just have one median?
// (2) how should I partition about the pivot once I get it?
}
public static int[] getMediansArray(int[] input, int[] medians) {
int numOfMedians = (int) Math.ceil(input.length/5.0);
int[] five = new int[5];
for (int i = 0; i < numOfMedians; i++) {
if (i != numOfMedians - 1) {
for (int j = 0; j < 5; j++) {
five[j] = input[(i*5)+j];
}
medians[i] = getMedian(five);
} else {
int numOfRemainders = input.length % 5;
int[] remainder = new int[numOfRemainders];
for (int j = 0; j < numOfRemainders; j++) {
remainder[j] = input[(i*5)+j];
}
medians[i] = getMedian(five);
}
}
return medians;
}
public static int getMedian(int[] input) {
Arrays.sort(input);
if (input.length % 2 == 0) {
return (input[input.length/2] + input[input.length/2 - 1]) / 2;
}
return input[input.length/2];
}
