题目：
https://leetcode.com/problems/distinct-subsequences/?tab=Description
一般没有明显思路的情况下，都要想想DP，用下Divide-and-Conque
下面的思路很好，很清晰
https://discuss.leetcode.com/topic/9488/easy-to-understand-dp-in-java/2
一个矩阵，如果字符不一样，那就用左侧的；如果字符一样，那就左侧+上方的。
An example: S: [acdabefbc] and T: [ab] first we check with a: * * S = [acdabefbc] mem[1] = [0111222222] then we check with ab: * * ] S = [acdabefbc] mem[1] = [0111222222] mem[2] = [0000022244]
原文：http://www.cnblogs.com/charlesblc/p/6443355.html