Solve stock profit and vertical tree traversal

You have a 60-minute coding interview with two algorithm questions: 1) **Max profit from one stock trade** - Input: an integer array `prices`, where `prices[i]` is the stock price on day `i`. - Task: Choose **one** day to buy and a **later** day to sell to maximize profit. Return the maximum profit; if no profitable trade is possible, return `0`. 2) **Vertical traversal of a binary tree** - Input: the root of a binary tree. - Define coordinates: root at `(row=0, col=0)`, left child `(row+1, col-1)`, right child `(row+1, col+1)`. - Task: Return the nodes grouped by vertical columns from leftmost `col` to rightmost. - Within each column, order nodes by `row` ascending (top to bottom). - If multiple nodes share the same `(row, col)`, order those nodes by their value ascending. - Output: a list of lists of node values following this ordering.