Recursion and Memoization

You are climbing a staircase with n steps. Each time you can climb either 1 or 2 steps. Return the number of distinct ways you can climb to the top.

You are a robber planning to rob houses along a street. Each house holds some money: nums[i] for the i-th house. The houses have a connected alarm system, so robbing two adjacent houses on the same night triggers the police. Return the maximum amount of money you can steal without ever robbing two adjacent houses.

Given an array of non-negative integers nums and an integer target, return the number of different expressions you can build by placing + or - before each integer in nums such that the resulting expression evaluates to target.