SOURCE

function merge( A, m, B, n ) {
    // write code here
    let i = 0;
    let j = 0;
    let res = [];
    while(true) {
        res.push(A[i]<B[j] ? A[i++] : B[j++]);
        if (i === m -1) {
            while(j < n-1){
                res.push(B[j++]);
            }
        }
        if (j === n-1) {
            while(i < m-1){
                res.push(A[i++]);
            }
        }
        if (res.length === m +n) {
            return res;
        }
    }
    
}
// [4,5,6],3, [1,2,3],3