归并排序

/**
 * Created by icecookstar on 2015/11/3.
 * 归并排序
 */
public class MergeSort {

    private static void merge(int[] matrix, int first, int middle, int last) {
        int[] tmp = new int[last - first + 1];
        int i = first;
        int m = middle;
        int j = middle + 1;
        int n = last;
        int k = 0;
        while (i <= m && j <= n) {
            if (matrix[i] <= matrix[j]) {
                tmp[k++] = matrix[i++];
            } else {
                tmp[k++] = matrix[j++];
            }
        }

        while (i <= m) {
            tmp[k++] = matrix[i++];
        }

        while (j <= n) {
            tmp[k++] = matrix[j++];
        }
        for (int l = 0; l < k; l++) {
            matrix[first + l] = tmp[l];
        }
    }

    private static void mergeSort(int[] matrix, int i, int j) {
        if (i < j) {
            int middle = (i + j) / 2;
            mergeSort(matrix, i, middle);
            mergeSort(matrix, middle + 1, j);
            merge(matrix, i, middle, j);
        }
    }

    public static void main(String[] args) {
        int[] matrix = new int[]{1, 3, 5, 4, 8, 10, 9, 20, 18, 18, 10};
        mergeSort(matrix, 0, matrix.length - 1);
        for (int i : matrix) {
            System.out.print(i + " ");
        }
    }
}