A contract to split funds between addresses. Demostrates pushing vs pulling transfers

Splitter.sol

pragma solidity ^0.4.6;

contract Splitter {

    mapping(address => uint) public balances;

    function unsafeSplit(address address1, address address2)
        public
        payable
        returns(bool success)
    {
	require(msg.value > 1);
	require(address1 != address(0));
	require(address2 != address(0));
        uint amount = (msg.value - (msg.value % 2)) / 2;        
        address1.transfer(amount);                       // if either transfer fails, the function stops executing
        address2.transfer(amount);                       // 
        msg.sender.transfer(msg.value % 2);
        return true;
    }


    function split(address address1, address address2)  // no external calls, so it will not fail
	public
	payable
	returns(bool success)
    {
	require(2 <= msg.value);
	require(msg.value % 2 == 0);
	require(address1 != address(0));
	require(address2 != address(0));
        uint amount = msg.value / 2;
        balances[address1] += amount;
        balances[address2] += amount;
	return true;
    }

    function withdraw()
	public
	returns(bool success)
    {
	require(0 < balances[msg.sender]);
	uint256 amountToTransfer = balances[msg.sender];
	balances[msg.sender] = 0;
	msg.sender.transfer(amountToTransfer);
	return true;
    }

}