C language for linear expected time Selection

In other words, the question of selecting the nth minimum is previously feared. I have read this article today. <ata> I have benefited a lot from this issue. although I have been writing a simple selection question for an hour, I only know if I really understand it when I implement the code. moreover, this item cannot be written in a sentence in the memory area.

The idea is to constantly find an exact position in the current array, to know how many elements before the current position are less than or equal to the value at the position, and then compare the position with the target position. narrow down the scope to achieve the goal.

In terms of running time, It is θ (n). The analysis process is very math and I will not make an axe.

Stick it up. My head feels a bit dull.

/* 2011-05-02-19.w.c -- expected Linear Time Selection */<br/> # include <stdio. h> </P> <p> # define size (20) </P> <p> int main (void); <br/> int select (int * const array, const int left, const int right, const int ith); <br/> int partition (int * const array, const int left, const int right ); <br/> void swap (int * const PLV, int * const PRV); </P> <p> int main (void) <br/> {<br/> int array [size] = {5, 6, 7, 9, 8, 4, 3, 2, 1, 10, 12, 11, 13, 14, 15, 16, 17, 19, 18, 20 }; <br/> int size = size; <br/> int ith = 19; </P> <p> printf ("the % d % s least number is: % d/N", ith, ith> 3? "Th": (1 = ith? "St": (2 = ith? "Nd": "RD"), select (array, 0, size-1, ith); </P> <p> return 0; <br/>}</P> <p> int select (int * const array, const int left, const int right, const int ith) <br/>{< br/> int trim, KTH; </P> <p> If (Left = right) <br/> return array [left]; <br/> partition = partition (array, left, right); <br/> kth = trim-left + 1; <br/> If (ith = kth) <br/> return array [th]; <br/> else if (ith <KTH) <br/> return Select (array, left, lower-1, ith); <br/> else <br/> return select (array, lower + 1, right, ith-KTH ); <br/>}</P> <p> int partition (int * const array, const int left, const int right) <br/>{< br/> int partition, i, J; </P> <p> align = right; <br/> I = left; <br/> J = right-1; <br/> while (1) <br/> {<br/> while (I! = Right & array [I] <array [distinct]) <br/> I ++; <br/> while (J! = Left & array [J]> = array [distinct]) <br/> j --; <br/> if (I <j) <br/> swap (array + I, array + J); <br/> else <br/> break; <br/>}< br/> swap (array + I, array + callback); </P> <p> return I; <br/>}</P> <p> void swap (int * const PLV, int * const PRV) <br/>{< br/> int temp; </P> <p> temp = * PLV; <br/> * PLV = * PRV; <br/> * PRV = temp; <br/>}