69. x 的平方根
Easy | Math, Binary Search
Math
70. 爬楼梯
Easy | Math, Dynamic Programming, Memoization
89. 格雷编码
Medium | Math, Backtracking, Bit Manipulation
9. 回文数
Easy | Math
96. 不同的二叉搜索树
Medium | Math, Dynamic Programming, Tree, Binary Search Tree, Binary Tree