
ZOJ Problem Set  2253
Given an m*n grid, you're required to fill it with the numbers from 1 to m*n but the following rules should be satisfied:
1. each number in grid is larger than its above; Now, I wonder how many distinct solutions I could make on a grid. For example. Consider such a 2*3 grid, we have the following solutions: 123 124 134 135 125 456 356 256 246 346 Thus, the sum is 5. Input Two positive integer m, n (0 < m, n < 10) per line. Two zeros indicate the end of input. Output A single integer per line for each case  the number of distinct solutions. Sample Input 2 3 Sample Output 5
Author: HE, Tao Source: ZOJ Monthly, November 2004 