oral_quiz->#排序数组中数字出现的次数#

最新推荐文章于 2025-12-17 05:58:59 发布

转载最新推荐文章于 2025-12-17 05:58:59 发布 · 105 阅读

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原文链接：https://my.oschina.net/ITHaozi/blog/282312

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#python

本文介绍了一种高效的方法来查找已排序数组中特定元素首次和末次出现的位置，并据此计算该元素出现的总次数。通过递归二分搜索算法实现，提供了完整的C语言代码实现及测试案例。

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#include <stdio.h>

bool g_bRightNumber = false;
void MyGetNumberHelp(int* data, int start, int end, int** first, int** last, int k);
int MyGetNumber(int* data, int length, int k) {
	g_bRightNumber = false;
	if(data == NULL || length <=0)
		return 0;

	int** first = &data;
	int* lastn = data+length-1;
	int** last = &lastn;
	MyGetNumberHelp(data, 0, length-1, first, last, k);

	int number = *last-*first+1;
	delete first;
	delete last;
	return g_bRightNumber ? number : 0;
}

void MyGetNumberHelp(int* data, int start, int end, int** first, int** last, int k) {
	if(start > end) return;

	int mid = (start+end) >> 1;
	if(data[mid] > k)
		MyGetNumberHelp(data, start, mid-1, first, last, k);
	else if(data[mid] < k)
		MyGetNumberHelp(data, mid+1, end, first, last, k);
	else {
		if(!g_bRightNumber)
			g_bRightNumber = true;
		if(mid>0 && mid<*last-data) {
			if(data[mid-1] < k) {
				*first = &data[mid];
				MyGetNumberHelp(data, start, mid-1, first, last, k);
			}
			else if(data[mid+1] > k) {
				*last = &data[mid];
				MyGetNumberHelp(data, mid+1, end, first, last, k);
			}
			else {
				MyGetNumberHelp(data, mid+1, end, first, last, k);
				MyGetNumberHelp(data, start, mid-1, first, last, k);
			}
		}
	}
}

//=========================hht's=============================
int GetFirstK(int* data, int length, int k, int start, int end) {
	if(start > end)
		return -1;

	int middleIndex = (start+end) >> 1;
	int middleData = data[middleIndex];

	if(middleData == k) {
		if((middleIndex > 0 && data[middleIndex-1] != k) || middleIndex == 0)
			return middleIndex;
		else
			end = middleIndex-1;
	}
	else if(middleData > k)
		end = middleIndex - 1;
	else
		start = middleIndex + 1;

	return GetFirstK(data, length, k, start, end);
}

int GetLastK(int* data, int length, int k, int start, int end) {
	if(start > end)
		return -1;

	int middleIndex = (start+end) >> 1;
	int middleData = data[middleIndex];

	if(middleData == k) {
		if((middleIndex < length-1 && data[middleIndex+1] != k) || middleIndex == length-1)
			return middleIndex;
		else
			start = middleIndex + 1;
	}
	else if(middleData < k)
		start = middleIndex + 1;
	else
		end = middleIndex - 1;

	return GetLastK(data, length, k, start, end);
}

int GetNumberOfK(int* data, int length, int k) {
	int number = 0;
	if(data != NULL && length >= 0) {
		int first = GetFirstK(data, length, k, 0, length-1);
		int last = GetLastK(data, length, k, 0, length-1);
		if(first > -1 && last > -1)
			number = last-first+1;
	}

	return number;
}


// ====================测试代码====================
void Test(const char* testName, int data[], int length, int k, int expected)
{
    if(testName != NULL)
        printf("%s begins: ", testName);

//    int result = MyGetNumber(data, length, k);
    int result = GetNumberOfK(data, length, k);
    if(result == expected)
        printf("Passed.\n");
    else
        printf("Failed.\n");
}

// 查找的数字出现在数组的中间
void Test1()
{
    int data[] = {1, 2, 3, 3, 3, 3, 4, 5};
    Test("Test1", data, sizeof(data) / sizeof(int), 3, 4);
}

// 查找的数组出现在数组的开头
void Test2()
{
    int data[] = {3, 3, 3, 3, 4, 5};
    Test("Test2", data, sizeof(data) / sizeof(int), 3, 4);
}

// 查找的数组出现在数组的结尾
void Test3()
{
    int data[] = {1, 2, 3, 3, 3, 3};
    Test("Test3", data, sizeof(data) / sizeof(int), 3, 4);
}

// 查找的数字不存在
void Test4()
{
    int data[] = {1, 3, 3, 3, 3, 4, 5};
    Test("Test4", data, sizeof(data) / sizeof(int), 2, 0);
}

// 查找的数字比第一个数字还小，不存在
void Test5()
{
    int data[] = {1, 3, 3, 3, 3, 4, 5};
    Test("Test5", data, sizeof(data) / sizeof(int), 0, 0);
}

// 查找的数字比最后一个数字还大，不存在
void Test6()
{
    int data[] = {1, 3, 3, 3, 3, 4, 5};
    Test("Test6", data, sizeof(data) / sizeof(int), 6, 0);
}

// 数组中的数字从头到尾都是查找的数字
void Test7()
{
    int data[] = {3, 3, 3, 3};
    Test("Test7", data, sizeof(data) / sizeof(int), 3, 4);
}

// 数组中的数字从头到尾只有一个重复的数字，不是查找的数字
void Test8()
{
    int data[] = {3, 3, 3, 3};
    Test("Test8", data, sizeof(data) / sizeof(int), 4, 0);
}

// 数组中只有一个数字，是查找的数字
void Test9()
{
    int data[] = {3};
    Test("Test9", data, sizeof(data) / sizeof(int), 3, 1);
}

// 数组中只有一个数字，不是查找的数字
void Test10()
{
    int data[] = {3};
    Test("Test10", data, sizeof(data) / sizeof(int), 4, 0);
}

// 鲁棒性测试，数组空指针
void Test11()
{
    Test("Test11", NULL, 0, 0, 0);
}

int main(int argc, char* argv[])
{
    Test1();
    Test2();
    Test3();
    Test4();
    Test5();
    Test6();
    Test7();
    Test8();
    Test9();
    Test10();
    Test11();

    return 0;
}

转载于:https://my.oschina.net/ITHaozi/blog/282312