Matrix Traversal

Given an m × n integer matrix, return an array of all the elements of the matrix in diagonal order — traversing each anti-diagonal alternately upward and downward.

Given an m × n matrix, return all elements of the matrix in spiral order: start at the top-left and traverse right, then down, then left, then up, repeating inward until every element is visited.

Given an m × n integer matrix, if an element is 0, set its entire row and column to 0. Do it in-place, and aim for O(1) extra space (use the first row/column as marker storage).