5月4日，ArrayTranspose，每日20行。

public class ArrayTranspose {    public static void transpose(int[][] m){        if(m == null)            return;        int temp;        for(int i = 0; i < m.length; i++){            for(int j = 0; j < m.length; j++){                if(i > j){                    temp = m[i][j];                    m[i][j] = m[j][i];                    m[j][i] = temp;                }            }        }    }    public static void print(int[][] m){        if(m == null)            return;        for(int i = 0; i < m.length; i++){            for(int j = 0; j < m.length; j++){                System.out.print(m[i][j] + " ");            }            System.out.println("");        }    }    public static void main(String[] args) {        int[][] t = {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}};        print(t);        transpose(t);        System.out.println("转置后的矩阵为：");        print(t);    }}