Given a matrix A, return the transpose of A. The transpose of a matrix is the matrix flipped over it's main diagonal, switching the row and column indices of the matrix. Example 1: ``` Input: [[1,2,3],[4,5,6],[7,8,9]] Output: [[1,4,7],[2,5,8],[3,6,9]] ``` Example 2: ``` Input: [[1,2,3],[4,5,6]] Output: [[1,4],[2,5],[3,6]] ``` Note: ``` 1 <= A.length <= 1000 1 <= A[0].length <= 1000 ``` ``` var transpose = function(A) { var A_ = []; for (var l = 0; l < A[0].length; l++) { // 二维数组初始化 A_[l] = []; } for(var i = 0; i < A.length; i++) { for(var j = 0; j < A[0].length; j++) { A_[j][i] = A[i][j]; } } return A_; } ```