right
right:it is about carry
right:it is a question about recursion
right:use the first row and column to decrease to O(1)
right
right:donnot use memset right way
wrong:but i know how to modify
right:not right at first
right:two traversal from left add from right
right:remove the duplicate element
right:donnot forget the status that the first element is deleted
right:haha accept once
wrong......