顺时针旋转矩阵
public int[][] rotateMatrix(int[][] mat, int n) {
// write code here
int[][] nums=new int[n][n];
if(n==0||mat==null) return nums;
for (int i=0;i<n;i++){
for (int j=0;j<n;j++){
nums[i][n-j-1]=mat[j][i];
}
}
return nums;
}