378.有序矩阵中第K小的元素

class Solution {
    public int kthSmallest(int[][] matrix, int k) {
        int rows = matrix.length, cols = matrix[0].length;
        int[] result = new int[rows * cols];
        int index = 0;
        for (int[] row : matrix) {
            for (int num : row) {
                result[index++] = num;
            }
        }
        Arrays.sort(result);
        return result[k - 1];
    }
}