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Kotlin-based LeetCode algorithm problem solutions, regularly updated
494\. Target Sum
Medium
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, which evaluates to `target`.
**Example 1:**
**Input:** nums = [1,1,1,1,1], target = 3
**Output:** 5
**Explanation:** There are 5 ways to assign symbols to make the sum of nums be target 3.
-1 + 1 + 1 + 1 + 1 = 3
+1 - 1 + 1 + 1 + 1 = 3
+1 + 1 - 1 + 1 + 1 = 3
+1 + 1 + 1 - 1 + 1 = 3
+1 + 1 + 1 + 1 - 1 = 3
**Example 2:**
**Input:** nums = [1], target = 1
**Output:** 1
**Constraints:**
* `1 <= nums.length <= 20`
* `0 <= nums[i] <= 1000`
* `0 <= sum(nums[i]) <= 1000`
* `-1000 <= target <= 1000`