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feat: add C merge sort (#434)

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* feat: add C merge sort

* Update merge_sort.c

---------

Co-authored-by: Yudong Jin <krahets@163.com>
This commit is contained in:
Guanngxu
2023-03-23 19:10:33 +08:00
committed by GitHub
parent 0a4a846e13
commit 9b0bdd929f
2 changed files with 62 additions and 0 deletions
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2
codes/c/chapter_sorting/CMakeLists.txt
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@ -3,3 +3,5 @@ add_executable(insertion_sort insertion_sort.c)
add_executable(quick_sort quick_sort.c) add_executable(quick_sort quick_sort.c)
add_executable(counting_sort counting_sort.c) add_executable(counting_sort counting_sort.c)
add_executable(radix_sort radix_sort.c) add_executable(radix_sort radix_sort.c)
add_executable(merge_sort merge_sort.c)

60
codes/c/chapter_sorting/merge_sort.c Normal file
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@ -0,0 +1,60 @@
/**
* File: merge_sort.c
* Created Time: 2022-03-21
* Author: Guanngxu (446678850@qq.com)
*/
#include "../include/include.h"
/* 合并左子数组和右子数组 */
// 左子数组区间 [left, mid]
// 右子数组区间 [mid + 1, right]
void merge(int *nums, int left, int mid, int right) {
int index;
// 初始化辅助数组
int tmp[right + 1 - left];
for(index = left; index < right + 1; index++) {
tmp[index - left] = nums[index];
}
// 左子数组的起始索引和结束索引
int leftStart = left - left, leftEnd = mid - left;
// 右子数组的起始索引和结束索引
int rightStart = mid + 1 - left, rightEnd = right - left;
// i, j 分别指向左子数组、右子数组的首元素
int i = leftStart, j = rightStart;
// 通过覆盖原数组 nums 来合并左子数组和右子数组
for (int k = left; k <= right; k++) {
// 若“左子数组已全部合并完”，则选取右子数组元素，并且 j++
if (i > leftEnd)
nums[k] = tmp[j++];
// 否则，若“右子数组已全部合并完”或“左子数组元素 <= 右子数组元素”，则选取左子数组元素，并且 i++
else if (j > rightEnd || tmp[i] <= tmp[j])
nums[k] = tmp[i++];
// 否则，若“左右子数组都未全部合并完”且“左子数组元素 > 右子数组元素”，则选取右子数组元素，并且 j++
else
nums[k] = tmp[j++];
}
}
/* 归并排序 */
void mergeSort(int *nums, int left, int right) {
// 终止条件
if (left >= right) return; // 当子数组长度为 1 时终止递归
// 划分阶段
int mid = (left + right) / 2; // 计算中点
mergeSort(nums, left, mid); // 递归左子数组
mergeSort(nums, mid + 1, right); // 递归右子数组
// 合并阶段
merge(nums, left, mid, right);
}
/* Driver Code */
int main() {
/* 归并排序 */
int nums[] = { 7, 3, 2, 6, 0, 1, 5, 4 };
int size = sizeof(nums) / sizeof(int);
mergeSort(nums, 0, size - 1);
printf("归并排序完成后 nums = ");
printArray(nums, size);
return 0;
}