摘要：
There is an m by n grid with a ball. Given the start coordinate (i,j) of the ball, you can move the ball to adjacent cell or cross the grid boundary i 阅读全文
摘要：
Given a positive integer n, return the number of all possible attendance records with length n, which will be regarded as rewardable. The answer may b 阅读全文
摘要：
You are given a string representing an attendance record for a student. The record only contains the following three characters: 'A' : Absent. 'L' : L 阅读全文