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.