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The problem You are given an integer array nums and an integer target. You want to build an expression out of nums by adding one of the symbols '+' and '-' before each integer in nums and then concatenate all the integers. For example, if nums = [2, 1], you can add a '+' before 2 and a '-' before 1 and concatenate them to build the expression "+2-1". Return the number of different expressions that you can build that evaluate to target. ...

The problem You are given an integer array coins representing coins of different denominations and an integer amount representing a total amount of money. Return the number of combinations that make up that amount. If that amount of money cannot be made up by any combination of the coins, return 0. You may assume that you have an infinite number of each kind of coin. The answer is guaranteed to fit into a signed 32-bit integer. ...

The problem You are given an array prices where prices[i] is the price of a given stock on the i-th day. Find the maximum profit you can achieve. You may complete as many transactions as you like (i.e., buy one and sell one share of the stock multiple times) with the following restrictions: After you sell your stock, you cannot buy stock on the next day (i.e., cooldown one day). Note: You may not engage in multiple transactions simultaneously (i.e., you must sell the stock before you buy again). ...

The problem Given an integer array nums, return true if you can partition the array into two subsets such that the sum of the elements in both subsets is equal, or false otherwise. Examples Input: nums = [1,5,11,5] Output: true Explanation: The array can be partitioned as [1, 5, 5] and [11]. Input: nums = [1,2,3,5] Output: false Explanation: The array cannot be partitioned into equal sum subsets. Constraints 1 <= nums.length <= 200 1 <= nums[i] <= 100 Explanation From the description of the problem, we learn that we are given a non-empty array nums that contains only positive integers, and we want to find out if we can partition the array into two different subsets such that the sum of each subset is equal. ...

The problem There are n cities connected by some number of flights. You are given an array flights where flights[i] = [from_i, to_i, price_i] indicates that there is a flight from city from_i to city to_i with cost price_i. You are also given three integers src, dst, and k, return the cheapest price from src to dst with at most k stops. If there is no such route, return -1. ...