最小的k个数

（O（n））

/*
最小的k个数
by Rowandjj
2014/8/9
*/
#include<stdio.h>
#include<stdlib.h>
int partition(int arr[],int low,int high)
{
	int val = arr[low];
	while(low < high)
	{
		while(low < high && arr[high] >= val)
		{
			high--;
		}
		arr[low] = arr[high];
		while(low < high && arr[low] <= val)
		{
			low++;
		}
		arr[high] = arr[low];
	}
	arr[low] = val;
	return low;
}
//获取最小的k个数
void GetLeastNumbers(int input[],int n,int output[],int k)
{
	if(input == NULL || output == NULL || n<=0 || k<=0 || k > n)
	{
		return;
	}
	int low = 0,high = n-1;
	int index = partition(input,low,high);
	while(index != k-1)
	{
		if(index > k-1)
		{
			high = index - 1;
			index = partition(input,low,high);
		}else
		{
			low = index+1;
			index = partition(input,low,high);
		}
	}
	for(int i = 0; i < k; i++)
	{
		output[i] = input[i];
	}
}
//-------------------------
//这题要求最小的k个数保持有序，故而使用快排对其进行排序
void QuickSort(int arr[],int low,int high)
{
	if(arr == NULL || low >= high)
	{
		return;
	}
	int index = partition(arr,low,high);
	QuickSort(arr,low,index-1);
	QuickSort(arr,index+1,high);
}
int main()
{
	int n,k;
	int output[200000];
	while(scanf("%d %d",&n,&k) != EOF)
	{
		if(n <= 0 || k <= 0 || k > n)
		{
			continue;
		}
		int *arr = (int*)malloc(sizeof(int)*n);
		if(!arr)
		{
			exit(-1);
		}
		for(int i = 0; i < n; i++)
		{
			scanf("%d",arr+i);
		}
		GetLeastNumbers(arr,n,output,k);
		QuickSort(output,0,k-1);
		for(int j = 0; j < k; j++)
		{
			if(j == k-1)
			{
				printf("%d\n",output[j]);
			}else
			{
				printf("%d ",output[j]);
			}
			
		}
                free(arr);
	}
	return 0;
}

/*
最小的k个数
by Rowandjj
2014/8/10
*/
#include<stdio.h>
#include<stdlib.h>
void HeapAdjust(int arr[],int start,int end)
{
	if(arr == NULL || start < 0 || end <= 0 || start >= end)
	{
		return;
	}
	int temp = arr[start];
	int i = start*2+1;
	while(i <= end)
	{
		if(i+1<=end && arr[i+1]>arr[i])
		{
			i++;
		}
		if(temp > arr[i])
		{
			break;
		}
		arr[start] = arr[i];
		start = i;
		i = i*2+1;
	}
	arr[start] = temp;
}
bool GetLeastNumbers(int input[],int n,int output[],int k)
{
	if(input == NULL || output == NULL || n <= 0 || k <= 0 || k > n)
	{
		return false;
	}
	int count = 0;
	bool needBuildHeap = true;
	for(int i = 0; i < n; i++)
	{
		if(count < k)
		{
			output[count++] = input[i];
		}else
		{		
			//第一次须要总体建堆
			if(needBuildHeap)
			{
				for(int j = k/2-1;j >= 0; j--)//建堆,从第一个非叶子结点開始
				{
					HeapAdjust(output,j,k-1);
				}
				needBuildHeap = false;
			}
			//大顶堆建好之后，比較当前遍历的整数与堆顶元素大小
			if(input[i] >= output[0])//大于等于堆顶元素
			{
				continue;//舍弃
			}
			//假设比堆顶元素小，那么须要交换
			output[0] = input[i];
			HeapAdjust(output,0,k-1);//又一次调整为大顶堆
		}				
	}
	return true;
}
//------------------------------------------
//由于要求从小到大排序，故而这里来一个堆排序
void HeapSort(int arr[],int len)
{
	if(arr == NULL || len <= 1)
	{
		return;
	}
	int i;
	for(i = len/2-1; i >= 0; i--)
	{
		HeapAdjust(arr,i,len-1);
	}
	for(i = len-1; i > 0; i--)
	{
		int temp = arr[0];
		arr[0] = arr[i];
		arr[i] = temp;
		HeapAdjust(arr,0,i-1);
	}
}
int main()
{
	int n,k;
	while(scanf("%d %d",&n,&k) != EOF)
	{
		if(n <= 0 || k <= 0)
		{
			continue;
		}
		int output[200000];
		int *arr = (int*)malloc(sizeof(int)*n);
		if(!arr)
		{
			exit(-1);
		}
		int i;
		for(i = 0; i < n; i++)
		{	
			scanf("%d",arr+i);
		}
		GetLeastNumbers(arr,n,output,k);
		HeapSort(output,k);
		for(i = 0; i < k; i++)
		{
			if(i == k-1)
			{
				printf("%d\n",output[i]);
			}else
			{
				printf("%d ",output[i]);
			}
			
		}
		free(arr);
	}
	return 0;
}