Leftmost Column with at Least a One

You are given a binary matrix with rows sorted in non-decreasing order. Implement a function to return the index of the leftmost column with at least a 1 in it. If no such column exists, return -1. The matrix is only accessible via a BinaryMatrix interface with the following methods: - get(row, col): returns the value at that cell (0 or 1) - dimensions(): returns [rows, cols]