package strategy;

import java.util.Arrays;

public class MergeSort implements SortStrategy {
    @Override
    public void sort(int[] data) {
        System.out.println("  [MergeSort] O(n log n) — stable, good for large datasets");
        mergeSort(data, 0, data.length - 1);
    }

    private void mergeSort(int[] a, int l, int r) {
        if (l >= r) return;
        int m = (l + r) / 2;
        mergeSort(a, l, m); mergeSort(a, m + 1, r);
        merge(a, l, m, r);
    }

    private void merge(int[] a, int l, int m, int r) {
        int[] left = Arrays.copyOfRange(a, l, m + 1);
        int[] right = Arrays.copyOfRange(a, m + 1, r + 1);
        int i = 0, j = 0, k = l;
        while (i < left.length && j < right.length)
            a[k++] = left[i] <= right[j] ? left[i++] : right[j++];
        while (i < left.length)  a[k++] = left[i++];
        while (j < right.length) a[k++] = right[j++];
    }

    @Override public String getName() { return "MergeSort"; }
}