大整数求和

前言

如果整数过大如何求值，比如说"4654564646547897891", "12315456456454564"

这时候常规整数装不下!

代码

方案一:

public static string bigNumberSum(string bigNumberA, string bigNumberB)
{
	int maxLength = bigNumberA.Length > bigNumberB.Length ? bigNumberA.Length : bigNumberB.Length;
	int[] arrayA = new int[maxLength+1];
	for (var i = 0; i < maxLength+1; i++)
	{
		if (bigNumberA.Length - 1 - i >= 0)
		{
			arrayA[i] = bigNumberA[bigNumberA.Length - 1 - i] - '0';
		}
		else
		{
			arrayA[i] = 0;
		}
	   
	}
	int[] arrayB = new int[maxLength+1];
	for (var i = 0; i < maxLength+1; i++)
	{
		if (bigNumberB.Length - 1 - i >= 0)
		{
			arrayB[i] = bigNumberB[bigNumberB.Length - 1 - i] - '0';
		}
		else
		{
			arrayB[i] = 0;
		}
	}
	int[] result = new int[maxLength+1];
	for (var i = 0; i < maxLength; i++)
	{
		var temp = result[i];
		temp = temp + arrayA[i] + arrayB[i];
		if (temp>10)
		{
			temp = temp - 10;
			result[i + 1] = 1;
		}
		result[i] = temp;
	}
	var hasup = 1;
	if (result[maxLength] == 1)
	{
		hasup = 0;
	}
	StringBuilder sb = new StringBuilder();
	for (var i = result.Length-1- hasup; i >=0; i--)
	{
		sb.Append(result[i]);
	}
	return sb.ToString();
}

static void Main(string[] args)
{
	Console.WriteLine(bigNumberSum("465456464654789789", "12315456456454564"));
	Console.ReadKey();
}

优化方案二：
九个一组:

public static string bigNumberSum(string bigNumberA, string bigNumberB)
{
	int maxLength = bigNumberA.Length > bigNumberB.Length ? bigNumberA.Length : bigNumberB.Length;
	var length =Convert.ToInt32(Math.Ceiling(Convert.ToDouble(maxLength) / 9));
	int[] arrayA = new int[length];
	for (var i = 0; i < length; i++)
	{
		if (i * 9 + 9 > bigNumberA.Length)
		{
			if (i * 9 <= bigNumberA.Length-1)
			{
				arrayA[i] = Convert.ToInt32(bigNumberA.Substring(bigNumberA.Length - 1 - 9 * i-(bigNumberA.Length - i * 9)+1, bigNumberA.Length - i * 9));
			}
			else
			{
				arrayA[i] = 0;
			}
		}
		else
		{
			arrayA[i] = Convert.ToInt32(bigNumberA.Substring(bigNumberA.Length - 1 - 9 * i-9+1, 9));
		}
	}
	int[] arrayB = new int[length];
	for (var i = 0; i < length; i ++)
	{
		if (i * 9 + 9 > bigNumberB.Length)
		{
			if (i * 9 <= bigNumberB.Length - 1)
			{
				arrayB[i] = Convert.ToInt32(bigNumberB.Substring(bigNumberB.Length - 1 - 9 * i-(bigNumberB.Length - i * 9)+1, bigNumberB.Length - i * 9));
			}
			else
			{
				arrayB[i] = 0;
			}
		}
		else
		{
			arrayB[i] = Convert.ToInt32(bigNumberB.Substring(bigNumberB.Length-1-9*i-9+1, 9));
		}
	}
	int[] result = new int[length];
	for (var i = 0; i < length; i++)
	{
		result[i] =  arrayA[i] + arrayB[i];
	}
	StringBuilder sb = new StringBuilder();
	for (var i = result.Length-1; i >=0; i--)
	{
		sb.Append(result[i]);
	}
	return sb.ToString();
}

static void Main(string[] args)
{
	Console.WriteLine(bigNumberSum("4654564646547897891", "12315456456454564"));
	Console.ReadKey();
}
}