【数据结构与算法分析——C语言描述】练习1.1——选择问题

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

#define N 100

int select(int* arr, int n, int k);

void main()
{
	int i, value;
	int* arr;
	clock_t elapse;

	srand((unsigned)time(NULL));
	arr = (int* )malloc(sizeof(int)* N);
	for(i = 0; i < N; i++)
	{
		arr[i] = rand() % 1000;  //产生的随机数限制在1000之内
		printf("%d ", arr[i]);
	}
	printf("\n");
	elapse = clock();
	value = select(arr, N, N/2);
	elapse = clock() - elapse;
	printf("Value: %d, elapsed: %.4lfs\n", value, (double)elapse/1000);
	system("pause");
}

int select(int* arr, int n, int k)
{
	int i, j, t;
	int* tmp;
	tmp = (int *)malloc(sizeof(int)* k);
	for(i = 0; i < k; i++)             //读入k个元素并升序排列
	{
		tmp[i] = arr[i];
		for(j = i; j > 0; j--)
		{
			if(tmp[j] < tmp[j-1])
			{
				t = tmp[j];
				tmp[j] = tmp[j-1];
				tmp[j-1] = t;
			}
		}
	}
	printf("读入k个元素并升序排列：\n");
	for(i = 0; i < k; i++)
	{
		printf("%d ",tmp[i]);
	}
	printf("\n");
	for(i = k; i<n; i++)                //加入新元素并升序排列
	{
		if(arr[i] > tmp[0])
		{
			tmp[0] = arr[i];
			for(j = 0; j < k-1; j++)
			{
				if(tmp[j] > tmp[j+1])
				{
					t = tmp[j];
					tmp[j] = tmp[j+1];
					tmp[j+1] = t;
				}
			}
		}
	}
	printf("加入新元素并升序排列：\n");
	for(i = 0; i < k; i++)
	{
		printf("%d ",tmp[i]);
	}
	printf("\n");
	return tmp[k-1];
}