使用动态数组，每次都重新分配内存
另有递归写法（注释部分），感觉应该没有问题但是总会超时


#include <iostream>
#include<algorithm>
#include<string>
using namespace std;

//int findSame(string a, string b)
//{
//	if (a == "" || b == "") return 0;
//	if (a[0] == b[0])
//	{
//		return 1 + findSame(a.substr(1), b.substr(1));
//	}
//	return max(findSame(a.substr(1), b), findSame(a, b.substr(1)));
//}


//开始用递归但一直超时，改为数组

int main()
{
	string x, y;
	int** result, size_x, size_y, i, j;
	while (cin >> x >> y)
	{
		size_x = x.size(); size_y = y.size();
		result = new int* [size_x + 1];
		for (i = 0; i <= size_x; i++)
		{
			result[i] = new int[size_y + 1];
			result[i][0] = 0;
		}
		for (j = 0; j <= size_y; j++) result[0][j] = 0;
		//result[i][j]代表考虑到x前i个，y前j个，的最大公共子串
		//第0行和第0列无实际意义，方便迭代，均设为0

		for (i = 1; i <= size_x; i++)
		{
			for (j = 1; j <= size_y; j++)
			{
				if (x[i - 1] == y[j - 1]) result[i][j] = result[i - 1][j - 1] + 1;
				else result[i][j] = max(result[i - 1][j], result[i][j - 1]);
			}
		}
		cout << result[size_x][size_y] << endl;
		for (i = 0; i <= size_x; i++) delete[]result[i];
		delete[] result;
	}
	
	return 0;
}