编程算法 - 最小的k个数 代码(C)

最小的k个数 代码(C)

本文地址: http://blog.csdn.net/caroline_wendy

题目: 输入n个整数, 找出其中的最小k个数.

使用快速排序(Quick Sort)的方法求解, 把索引值(index)指向前k个数.

代码:

/*
 * main.cpp
 *
 *  Created on: 2014.6.12
 *      Author: Spike
 */

/*eclipse cdt, gcc 4.8.1*/

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

int RandomInRange(int min, int max) {
	int random = rand() % (max-min+1) + min;
	return random;
}

void Swap (int* num1, int* num2) {
	int temp = *num1;
	*num1 = *num2;
	*num2 = temp;
}

int Partition(int data[], int length, int start, int end) {
	if (data == NULL || length <= 0 || start < 0 || end >= length)
		return -1;
	int index = RandomInRange(start, end);
	Swap(&data[index], &data[end]);
	int small = start-1;
	for (index = start; index < end; ++index) {
		if (data[index] < data[end]) {
			small++;
			if (small != index)
				Swap(&data[small], &data[index]);
		}
	}
	small++;
	Swap(&data[small], &data[end]);
	return small;
}

void GetLeastNumbers(int* input, int n, int* output, int k) {
	if (input == NULL || n <= 0 || output == NULL || k <= 0 || k>n)
		return;
	int start = 0;
	int end = n-1;
	int index = Partition(input, n, start, end);
	while (index != k-1) {
		if (index > k-1) {
			end = index - 1;
			index = Partition(input, n, start, end);
		} else {
			start = index + 1;
			index = Partition(input, n, start, end);
		}
	}
	for (int i=0; i<k; ++i) {
		output[i] = input[i];
	}
}

int main(void)
{
    int input[] =  {4, 5, 1, 6, 2, 7, 3, 8};
    int output[4];
    GetLeastNumbers(input, 8, output, 4);
    for (int i=0; i<4; ++i) {
    	printf("%d ", output[i]);
    }
    printf("\n");

    return 0;
}

输出:

1 2 3 4

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