计数排序

计数排序是一种非比较排序。

原理：

代码：

void CountSort(int* nums, int numsSize) {int max = nums[0], min = nums[0];for (int i = 0; i < numsSize; i++) {if (nums[i] > max) {max = nums[i];}if (nums[i] < min) {min = nums[i];}}int range = (max - min) + 1;int* count = (int*)malloc(sizeof(int) * range);memset(count, 0, sizeof(int) * range);//统计次数for (int i = 0; i < numsSize; i++) {count[nums[i] - min]++;//count[nums[i] ]++;}int j = 0;for (int i = 0; i < range; i++) {while (count[i]--) {nums[j++] = i + min;//nums[j++] = i;//++j;}}free(count);
}

for循环中i的范围应该注意，是range不是numsSize。

归并排序

原理：

 

代码：

void _MergeSort(int* nums, int left, int right,int*tmp) {if (left >= right) {return;}int mid = (left + right) >> 1;//[left,mid]  [mid+1,right]有序后，即可进行归并_MergeSort(nums, left, mid, tmp);_MergeSort(nums, mid+1, right, tmp);int begin1 = left, end1 = mid;int begin2 = mid + 1, end2 = right;int index = left;while (begin1 <= end1 && begin2 <= end2) {if (nums[begin1] < nums[begin2]) {tmp[index++] = nums[begin1++];}else {tmp[index++] = nums[begin2++];}}while (begin1 <= end1) {tmp[index++] = nums[begin1++];}while (begin2 <= end2) {tmp[index++] = nums[begin2++];}for (int i = left; i <= right; i++) {nums[i] = tmp[i];}
}
void MergeSort(int* nums, int numsSize) {int* tmp = (int*)malloc(sizeof(int) * numsSize);_MergeSort(nums, 0, numsSize - 1,tmp);free(tmp);
}

归并排序核心是利用_MergeSort，然后在_MergeSort中分区间递归。

递归后归并。最小区间例如【0,0】【1,1】选小的往下放，然后拷贝回原数组。