1428. Leftmost Column with at Least a One

1. (Binary Search) For each row do a binary search to find the leftmost one on that row and update the answer.

2. (Optimal Approach) Imagine there is a pointer p(x, y) starting from top right corner. p can only move left or down. If the value at p is 0, move down. If the value at p is 1, move left. Try to figure out the correctness and time complexity of this algorithm.