public class DayCode {    public static void main(String[] args) {        int[][] matrix = new int[][]{{1, 2, 3}, {4, 5, 6}, {7, 8, 9}};        int[][] ans = new DayCode().transpose(matrix);        System.out.println("ans is " + Arrays.deepToString(ans));    }
    /**     * https://leetcode-cn.com/problems/transpose-matrix/     * 时间复杂度 O (rows * cols)     * 空间复杂度 O (rows * cols)     * @param matrix     * @return     */    public int[][] transpose(int[][] matrix) {        int rows = matrix.length;        int cols = matrix[0].length;        int[][] ans = new int[cols][rows];        for (int r = 0; r < rows; r++) {            for (int c = 0; c < cols; c++) {                ans[c][r] = matrix[r][c];            }        }        return ans;    }}