C语言实现TopK

说明

由快速排序的衍生.

代码

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

#define MAX 30

int arr[MAX];

void quickSort(int arr[], int start, int end, int top);
int getIndex(int arr[], int start, int end);

int main(){
	srand(time(0));

	for(int i = 0; i < MAX; ++i){
		arr[i] = rand()%100;
		printf("%d ", arr[i]);
	}
	putchar('\n');

	int top;
	scanf("%d", &top);
	
	quickSort(arr, 0, MAX-1, top);

	for(int i = 0; i < MAX; ++i){
		printf("%d ", arr[i]);
	}


	return 0;
}

void quickSort(int arr[], int start, int end, int top){
	if(start < end){
		int index = getIndex(arr, start, end);

		if( index == top ){
			return;
		}else if( index > top ){
			quickSort(arr, start, index-1, top);
		}else if( index > top ){
			quickSort(arr, index+1, end, top);
		}
	}
}
int getIndex(int arr[], int start, int end){
	
	int key = arr[start];

	while(start < end){
		// 在队尾找到比Key值小的元素,
		while(start < end && key <= arr[end]){
			end--;
		}
		arr[start] = arr[end];
		
		// 在队头找到比Key值大的元素
		while(start < end && key >= arr[start]){
			start++;
		}
		arr[end] = arr[start];

	}
	// start 与 end 相等, 
	arr[start] = key;
	return start;

}