function merge(a, b) {
    const result = []
    
    let i = 0, j = 0; 
    
    while (i < a.length && j < b.length) {
        if (a[i] < b[j]) {
            result.push(a[i])
            i++
        } else {
            result.push(b[j])
            j++
        }
    }

    while (i < a.length) {
        result.push(a[i])
        i++
    }
    while (j < b.length) {
        result.push(b[j])
        j++
    }

    return result
}

function msort(items) {
    if (items.length < 2) {
        return items 
    }

    const a = msort(items.slice(0, Math.floor(items.length / 2)))
    const b = msort(items.slice(Math.floor(items.length / 2)))

    return merge(a, b)
}

// driver code
let a = [6,4,2]
let b = [5,3,1]
let c = merge(a, b)
console.log(c)
console.log(msort(c))