目录

1.堆排序

思考：建堆用向上调整建堆还是向下调整建堆？调堆用向上调整还是向下调整？

1.3总结：升序用大堆，降序用小堆。用向下调整建堆。

2.topK

2.3总结：要前k大，建小堆。要前k小，建大堆。

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1.堆排序

1.1分析

思考：建堆用向上调整建堆还是向下调整建堆？调堆用向上调整还是向下调整？

1.2代码参考：

//堆排序
void HeapSort(HPDataType* a, int n) {assert(a);//先建堆for (int i = (n - 1 - 1) / 2; i >= 0; i--) {AdjustDown(a, i, n);}//排序，用up还是down？用小堆还是大堆//用down// 结果要升序，用大堆。结果要降序，用小堆int end = n - 1;while (end > 0) {Swap(&a[0], &a[end]);		AdjustDown(a,0, end); --end;}}
int main() {int a[] = { 3,6,1,5,8,9,2,7,4,0 };HeapSort(a, sizeof(a) / sizeof(int));for (int i = 0; i < sizeof(a) / sizeof(int); i++) {printf("%d ",a[i]);}return 0;
}

1.3总结：升序用大堆，降序用小堆。用向下调整建堆。

2.topK

2.1分析：

2.2 代码参考：

//top k问题
void CreateNDate()
{//造数据int n = 10000;srand((unsigned int)time(NULL));const char* file = "data.txt";FILE* fin = fopen(file, "w");if (fin == NULL){perror("fopen error");return;}for (int i = 0; i < n; ++i){int x = (rand() + i) % 100000;fprintf(fin, "%d\n", x);}fclose(fin);
}
void topk()
{//获取kprintf("请输入k：");int k = 0;scanf("%d", &k);//先从文件中获取k个数据const char* file = "data.txt";FILE* fout = fopen(file, "r");if (fout == NULL){perror("fopen error");return;}int* minheap = (int*)malloc(sizeof(int) * k);if (minheap == NULL) {perror("malloc  fail ");return;}for (int i = 0; i < k; i++) {fscanf(fout, "%d", &minheap[i]);}//将k个数据，通过向下调整，建成小堆for (int i = (k - 1 - 1) / 2; i >= 0; i--) {AdjustDown(minheap, i, k);}//遍历文件剩余值(N-k)，如果碰见比堆顶大的数据，就入堆int x = 0;while (fscanf(fout, "%d", &x) != EOF){//读取剩余数据，比堆顶的值大，就替换他进堆if (x > minheap[0]) {minheap[0] = x;AdjustDown(minheap, 0, k);}		}//将top k打印出来for (int i = 0; i < k; i++) {printf("%d ", minheap[i]);}fclose(fout);
}
int main()
{	CreateNDate();topk();return 0;}

2.3总结：要前k大，建小堆。要前k小，建大堆。