【算法导论笔记】插入排序 && 归并排序

插入排序 时间复杂度 O(n^2)

#include "pch.h"
#include <iostream>

void insectionSort();

int origin[] = { 12, 15, 3, 2, 31, 34, 18, 9, 99, 121, 56 };

int main()
{
	insectionSort();
	for (int i = 0; i < sizeof(origin) / sizeof(origin[0]); i++)
	{
		std::cout << origin[i] << std::endl;
	}
}

void insectionSort()
{
	for (int i = 1; i < sizeof(origin) / sizeof(origin[0]); i++)
	{
		// 标记第 i 个做插入排序的元素，0 - i-1 已经是有序序列 
		int temp = origin[i];
		// 从 i-1 开始和前面排序序列比较，看在哪里插入
		int j = i - 1;
		for (; j >= 0 && origin[j] > temp; j--)
		{
			origin[j + 1] = origin[j];
		}
		// 最终的 j 标识插入的前一个位置
		origin[j + 1] = temp;
	}
}

归并排序 时间复杂度 O(nlogn)

#include "pch.h"
#include <iostream>

void mergeSort(int * A, int number);
void merge(int * A, int * L, int lIndex, int * R, int rIndex);

int main()
{
	int sequence[] = { 12, 15, 3, 2, 31, 34, 18, 9, 99, 121, 56 };
	int sizeOfElements = sizeof(sequence) / sizeof(sequence[0]);
	mergeSort(sequence, sizeOfElements);

	for (int i = 0; i < sizeOfElements; i++)
	{
		std::cout << sequence[i] << std::endl;
	}
}

/* 归并排序主代码 */
void mergeSort(int * A, int size)
{
	if (size < 2) return;
	int mid = size / 2;
	int *L, *R;

	L = new int[mid];
	R = new int[size - mid];

	for (int i = 0; i < mid; i++) L[i] = A[i];
	for (int i = mid; i < size; i++) R[i - mid] = A[i];

	mergeSort(L, mid);
	mergeSort(R, size - mid);
	merge(A, L, mid, R, size - mid);

	delete[] L;
	delete[] R;
}

/* 合并两个已排序的数组，最终返回给 A */
void merge(int * A, int * L, int lSize, int * R, int rSize)
{
	int lIndex = 0, rIndex = 0;

	for (int i = 0; i < lSize + rSize; i++)
	{
		if (lIndex >= lSize)
		{
			A[i] = R[rIndex++];
			continue;
		}
		if (rIndex >= rSize)
		{
			A[i] = L[lIndex++];
			continue;
		}

		if (L[lIndex] < R[rIndex]) 
		{
			A[i] = L[lIndex++];
		}
		else if (L[lIndex] == R[rIndex])
		{
			A[i] = L[lIndex++];
		}
		else if (L[lIndex] > R[rIndex])
		{
			A[i] = R[rIndex++];
		}
	}
}