动态规划问题。给定一个整数的二维数组，由其中若干邻近元素构成的矩形称为子数组。 编程计算所有子数组元素之和的最大值。输入为整数n，及n^2个数，输出为所有子数组元素之和的最大值-Dynamic programming problem.Given a two-dimensional array of positive and negative integers, a sub-rectangle is any contiguous sub-array of size 1*1 or greater located within the whole array. The sum of a rectangle is the sum of all the elements in that rectangle. In this problem the sub-rectangle with the largest sum is referred to as the maximal sub-rectangle.