Backward Digit Sums --- DFS+全排列

Time Limit: 1000MS		Memory Limit: 65536K
Total Submissions: 4946		Accepted: 2850

Description

FJ and his cows enjoy playing a mental game. They write down the numbers from 1 to N (1 <= N <= 10) in a certain order and then sum adjacent numbers to produce a new list with one fewer number. They repeat this until only a single number is left. For example, one instance of the game (when N=4) might go like this:

    3   1   2   4

      4   3   6

        7   9

         16

Behind FJ's b