集計ソートMerge Sort

4333 ワード

自分で書いたコードを記録してください
public class MergeSort {

//    recursive

    public static void mergeSort(int[] nums, int start, int end) {

        if(start >= end) {

            return;

        }

        int mid = (start + end) / 2;

        mergeSort(nums, start, mid);

        mergeSort(nums, mid + 1, end);

        merge(nums, start, mid, end);

    }



    public static void merge(int[] nums, int start, int mid, int end) {

        int[] temp = new int[end - start + 1];

        int i = start, j = mid + 1, k = 0;

        while(i <= mid && j <= end) {

            if(nums[i] <= nums[j]) {

                temp[k++] = nums[i++];

            } else {

                temp[k++] = nums[j++];

            }

        }

        while(i <= mid) {

            temp[k++] = nums[i++];

        }

        while(j <= end) {

            temp[k++] = nums[j++];

        }

        i = start;

        while(i <= end) {

            nums[i] = temp[i - start];

            i++;

        }

    }



//    itervative

    public static void mergeSort(int[] nums) {

        for(int gap = 1; gap < nums.length; gap *= 2) {

            for(int start = 0; start < nums.length; start += gap * 2) {

                merge(nums, start, Math.min(start + gap - 1, nums.length - 1), Math.min(start + gap * 2 - 1, nums.length - 1));

            }

        }

    }



    public static void main(String[] args) {

        int[] nums = new int[]{13, 6, 9, 1, 19, -21, 5};

        mergeSort(nums);

        System.out.println(nums);

    }

}