CareerCup

Please state question clearly.

What is given?
What is expected?
What is allowed/ not-allowed?

Use trie structure to store number and while typing the number traverse through all the nodes till all the leaves.

how about using a prefix tree (trie) data structure:
key #1 (1,2,3)
key #2 (4,5,6)
key #3 (7,8,9)
key #4 (0)
if dial 415-6789-5432 then dial 212-233... with automatic completion provided

There are about 200 countries. Each country have a) own country code (which starts with + sign), b) 10 digit phone identification number (vast majority of countries follow this standard).

Summarizing these facts we get 2 * 10^2 * 10^10 which is 2 * 10^12 total phone numbers in the world.

Enumerating is quite easy:
1. enumerate through countries phone codes (finite list of about 200 items)
2. run tenfold loop and output the string of a kind "+XX" (country code) "i0i1i2i3i4i5i6i7i8i9"

Watch for:
1. There are might be exceptions for some countries that might have 7 to 9 phone numbers internally
2. Some countries allow having alphabetical characters in a phone number (which are being translated to a digit ones through some centralized name stores)

There are about 200 countries. Each country have a) own country code (which starts with + sign), b) 10 digit phone identification number (vast majority of countries follow this standard).

Summarizing these facts we get 2 * 10^2 * 10^10 which is 2 * 10^12 total phone numbers in the world.

Enumerating is quite easy:
1. enumerate through countries phone codes (finite list of about 200 items)
2. run tenfold loop and output the string of a kind "+XX" (country code) "i0i1i2i3i4i5i6i7i8i9"

Watch for:
1. There are might be exceptions for some countries that might have 7 to 9 phone numbers internally
2. Some countries allow having alphabetical characters in a phone number (which are being translated to a digit ones through some centralized name stores)

void phoneNumbers(const string &dialString, string prefix) {

	if (diaString.length() == prefix.length()) {
		std::cout<<prefix<<endl;
	return;
}
	for (int i=0; i<9; i++) 
		phoneNumbers(diaString, prefix+(‘0’+i));
}