Traverse a tree and answer 2D prefix sums

You are given two independent coding tasks. ## Task 1: In-order traversal of a binary tree Given the root of a binary tree, return the in-order traversal of its node values. - **In-order** means: traverse left subtree → visit node → traverse right subtree. - **Input:** `root` (may be `null`) - **Output:** an array/list of node values in in-order - **Constraints (typical):** up to ~10^5 nodes; values fit in 32-bit int. ## Task 2: Sum of the top-left submatrix up to (x, y) Given an `m x n` matrix `A` of integers and coordinates `(x, y)` (0-indexed), compute the sum of all elements in the rectangle from `(0,0)` to `(x,y)` inclusive. Example: `sum(x,y) = Σ_{i=0..x} Σ_{j=0..y} A[i][j]` - **Input:** matrix `A`, and one or more queries `(x, y)` where `0 ≤ x < m`, `0 ≤ y < n` - **Output:** for each query, return the computed sum - **Follow-up (common):** If there are many queries, design for fast per-query time. - **Constraints (typical):** `m,n` up to ~10^3 or higher; values can be negative; sums may require 64-bit integer type.