/**

 * @param {number[][]} matrix

 * @return {number[]}

 */

var findDiagonalOrder = function(matrix) {

    if(matrix == []) return []

    let m = matrix.length

    let n = matrix[0].length

    let i=0,j=0

    let arr = []

    for(let l = 0;l<m*n;l++){

        arr.push(matrix[i][j])

        if((i+j)%2==0){

            if(j == n-1){

                i++

            }else if(i==0){

                j++

            }else{

                i--

                j++

            }

        }else{

            if(i == m-1){

                j++

            }else if(j == 0){

                i++

            }else{

                i++

                j--

            }

        }

    }

    return arr

};