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feat: add C merge sort (#434)
* feat: add C merge sort * Update merge_sort.c --------- Co-authored-by: Yudong Jin <krahets@163.com>
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@ -3,3 +3,5 @@ add_executable(insertion_sort insertion_sort.c)
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add_executable(quick_sort quick_sort.c)
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add_executable(counting_sort counting_sort.c)
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add_executable(radix_sort radix_sort.c)
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add_executable(merge_sort merge_sort.c)
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60
codes/c/chapter_sorting/merge_sort.c
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60
codes/c/chapter_sorting/merge_sort.c
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@ -0,0 +1,60 @@
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/**
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* File: merge_sort.c
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* Created Time: 2022-03-21
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* Author: Guanngxu (446678850@qq.com)
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*/
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#include "../include/include.h"
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/* 合并左子数组和右子数组 */
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// 左子数组区间 [left, mid]
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// 右子数组区间 [mid + 1, right]
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void merge(int *nums, int left, int mid, int right) {
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int index;
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// 初始化辅助数组
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int tmp[right + 1 - left];
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for(index = left; index < right + 1; index++) {
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tmp[index - left] = nums[index];
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}
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// 左子数组的起始索引和结束索引
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int leftStart = left - left, leftEnd = mid - left;
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// 右子数组的起始索引和结束索引
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int rightStart = mid + 1 - left, rightEnd = right - left;
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// i, j 分别指向左子数组、右子数组的首元素
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int i = leftStart, j = rightStart;
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// 通过覆盖原数组 nums 来合并左子数组和右子数组
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for (int k = left; k <= right; k++) {
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// 若“左子数组已全部合并完”,则选取右子数组元素,并且 j++
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if (i > leftEnd)
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nums[k] = tmp[j++];
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// 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++
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else if (j > rightEnd || tmp[i] <= tmp[j])
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nums[k] = tmp[i++];
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// 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++
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else
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nums[k] = tmp[j++];
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}
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}
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/* 归并排序 */
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void mergeSort(int *nums, int left, int right) {
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// 终止条件
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if (left >= right) return; // 当子数组长度为 1 时终止递归
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// 划分阶段
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int mid = (left + right) / 2; // 计算中点
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mergeSort(nums, left, mid); // 递归左子数组
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mergeSort(nums, mid + 1, right); // 递归右子数组
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// 合并阶段
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merge(nums, left, mid, right);
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}
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/* Driver Code */
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int main() {
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/* 归并排序 */
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int nums[] = { 7, 3, 2, 6, 0, 1, 5, 4 };
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int size = sizeof(nums) / sizeof(int);
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mergeSort(nums, 0, size - 1);
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printf("归并排序完成后 nums = ");
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printArray(nums, size);
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return 0;
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}
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