Section 1Understand Problem
Section 01
Understand the problem
Restate the problem precisely. Interviewers reward candidates who pause, define the contract, and name the guarantees before coding.
Problem statement
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. Return the number of different expressions that you can build, which evaluates to `target`.
Example
nums = [1,1,1,1,1], target = 3 → 5
Constraints
1 ≤ nums.length ≤ 20 · 0 ≤ nums[i] ≤ 1000 · −1000 ≤ target ≤ 1000
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