归并排序（一）

c语言版本：

cpp 复制代码

void MergeSort(int* array, int n)
{
	int* temp = (int*)malloc(sizeof(int) * n);
	if (NULL == temp)
	{
		assert(0);
		printf("fail\n");
	}
	_MergeSort(array, 0, n, temp);
}

void _MergeSort(int array[], int left, int right, int *temp)
{
	// 如果区间元素个数小于一个即不进行排序
	if (right - left <= 1)
		return;
	// 将数组分为左右俩个区间
	int mid = left + ((right - left) >> 1);
 
	// 递归遍历左右区间
	_MergeSort(array, left, mid, temp);
	_MergeSort(array, mid, right, temp);
 
	// 将左右区间元素进行归并
	MergeData(array, left, mid, right, temp);
	// 将辅助空间中的元素拷贝到原空间
	memcpy(array + left, temp + left, (right - left) * sizeof(int));
}

void MergeData(int array[], int left, int mid, int right, int* temp)
{
	int begin1 = left;
	int end1 = mid;
 
	int begin2 = mid;
	int end2 = right;
 
	// 数组的合并
	int index = left;
	while (begin1 < end1 && begin2 < end2)
	{
		if (array[begin1] <= array[begin2])
			temp[left++] = array[begin1++];
		else
			temp[left++] = array[begin2++];
	}
	while(begin1<end1)
		temp[left++] = array[begin1++];
	while(begin2<end2)
		temp[left++] = array[begin2++];
}

归并排序二叉树的后序遍历

c++版本

cpp 复制代码

class Solution {
public:
    vector<int> temp; // 全局temp用来还原数组
    void mergesort(int left, int right, vector<int>& nums)
    {
        if(left >= right) return; 
        int mid = left + ((right-left)>>1);
        mergesort(left, mid, nums);  // 合并【left，mid】
        mergesort(mid+1, right, nums); // 合并【mid+1，right】

        mergedata(left, mid, right, nums); // 合并数据
    }
    void mergedata(int left, int mid, int right, vector<int>& nums)
    {
        // 将left到mid 和 mid+1到right进行有序数组的合并
        int cur1 = left, cur2 = mid+1;
        int small = left;
        while(cur1 <= mid && cur2 <= right)
            temp[small++] = nums[cur1] <= nums[cur2] ? nums[cur1++] : nums[cur2++];
        // 处理没有访问到最后边界部分
        while(cur1 <= mid) 
            temp[small++] = nums[cur1++];
        while(cur2 <= right) 
            temp[small++] = nums[cur2++];
        // 将temp还原到nums  也可以直接返回temp
        for(int i = left; i <= right; i++)
            nums[i] = temp[i];
    }
    vector<int> sortArray(vector<int>& nums) {
        temp.resize(nums.size());
        mergesort(0, nums.size()-1, nums);
        return nums;
    }
};