0494.TargetSum.js

// 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

// 来源：力扣（LeetCode）
// 链接：https://leetcode-cn.com/problems/target-sum
// 著作权归领扣网络所有。商业转载请联系官方授权，非商业转载请注明出处。