Build a Target Stack from an Increasing Stream

### Problem Start with an empty stack and the stream 1,2,...,n. A "Push" consumes the next stream integer and places it on the stack; a "Pop" removes the nonempty stack's top. Produce an operation list that makes the stack, bottom to top, equal target. Stop immediately when target is reached: read no later integer and perform no later operation. Return any valid operation list. ```cpp class Solution { public: vector<string> buildArray(vector<int>& target, int n); }; ``` ### Examples **Example 1:** ```text Input: target = [2], n = 3 Output: ["Push","Pop","Push"] Explanation: Discard1,keep2,and stop before consuming3. ``` **Example 2:** ```text Input: target = [3], n = 3 Output: ["Push","Push","Pop","Pop","Push"] Explanation: Push1 and2,pop2 then1,and push3 to reach the target. Immediate push/pop pairs for1 and2 would also be valid. ``` ### Constraints - target has length 1 to 100. - `1 <= n <= 100` and `1 <= target[i] <= n`. - target is strictly increasing. ### Contract considerations The native result remains `vector<string>`; validity of the returned operation sequence is the substantive output contract. ```hint Read the boundary condition Check stream consumption, nonempty-stack pops, and immediate stopping when the target is first reached. Different legal operation lists remain acceptable. ``` ### What a Strong Answer Covers The native result remains `vector<string>`; validity of the returned operation sequence is the substantive output contract. ### Follow-up Questions Optional practice extension,separate from the original task: How would you validate an arbitrary returned operation list while enforcing immediate stopping?