Transpose of Matrix

import java.util.*;

class Solution {
    public ArrayList<ArrayList<Integer>> transpose(int[][] mat) {
        ArrayList<ArrayList<Integer>> list = new ArrayList<>();

        for (int i = 0; i < mat.length; i++) {
            ArrayList<Integer> temp = new ArrayList<>();
            for (int j = 0; j < mat[0].length; j++)
                temp.add(mat[j][i]);
            list.add(temp);
        }

        return list;
    }
}