In a binary matrix (all elements are `0` and `1`), every row is sorted in ascending order (`0` to the left of `1`). Find the leftmost column index with a `1` in it.\n\n**Example 1:**\n```\nInput:\n[[0, 0, 0, 1],\n [0, 0, 1, 1],\n [0, 1, 1, 1],\n [0, 0, 0, 0]]\nOutput: 1\n```\n\n**Example 2:**\n```\nInput:\n[[0, 0, 0, 0],\n [0, 0, 0, 0],\n [0, 0, 0, 0],\n [0, 0, 0, 0]]\nOutput: -1\n```\n\nExpected solution better than `O(r * c)`.\n\n<details> \n  <summary>Solution</summary>\n\nJava: https://leetcode.com/playground/oFDW7DqN\nTime complexity: `O(r + c)`.\nSpace complexity: `O(1)`.\n</details>\n\n<details> \n  <summary>Similar questions</summary>\n\n* https://leetcode.com/problems/leftmost-column-with-at-least-a-one/ (premium)\n* https://leetcode.com/problems/search-a-2d-matrix-ii\n</details>

In a binary matrix (all elements are 0 and 1), every row is sorted in ascending order (0 to the left of 1). Find the leftmost column index with a 1 in it.\n\nEx