Recursive Searching and Sorting · AP Computer Science A

AP Computer Science A Quiz

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For this recursive merge sort, what is the base case that stops further splitting of the array?

public class Sorter {
    public static void mergeSort(int[] nums, int left, int right) {
        // Base case: one element (or empty) segment is already sorted
        if (left >= right) {
            return;
        }

        int mid = (left + right) / 2;

        // Recursive step: sort both halves
        mergeSort(nums, left, mid);
        mergeSort(nums, mid + 1, right);

        // Merge sorted halves
        merge(nums, left, mid, right);
    }

    private static void merge(int[] nums, int left, int mid, int right) {
        int[] temp = new int[right - left + 1];
        int i = left;
        int j = mid + 1;
        int k = 0;

        // Merge elements in sorted order
        while (i <= mid && j <= right) {
            if (nums[i] <= nums[j]) {
                temp[k++] = nums[i++];
            } else {
                temp[k++] = nums[j++];
            }
        }
        while (i <= mid) {
            temp[k++] = nums[i++];
        }
        while (j <= right) {
            temp[k++] = nums[j++];
        }

        // Copy back
        for (int t = 0; t < temp.length; t++) {
            nums[left + t] = temp[t];
        }
    }
}

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