I am accessed by their recuiter from Singapore in LinkedIn.

And I passed the 1st round phone screen, the questions mainly focus on the experience I have and management I got, and the project I currently work. The other behavioral questions like what’s the point you like/dislike your current job?

I was scheduled to have technical phone interview with someone in US.

**Question:**

Add (insert) the mathematical operators `+`

or `-`

(plus or minus) before any of the digits in the decimal numeric string `"123456789"`

such that the resulting mathematical expression adds up to a particular `target`

sum. Return all possible combinations. https://rosettacode.org/wiki/Sum_to_100

**Example:**

`123 + 4 - 5 + 67 - 89 = 100`

I started with some easy case,like “1”,“12”…

to analyz how to trace back with subset

to generalize the case, finally i wrote a rough draft function

It took most of time to complete the cases, and when he asked me the complexity of the function I wrote.

I gave wrong answer…but time is up, he didn’t ask me to consider again.

I did my best, it’s still rejected.

This question is similar to https://leetcode.com/problems/expression-add-operators/ except that it do not use “*” here.