# Day 21 of 30-Day LeetCode Challenge

## A binary matrix means that all elements are `0`

or `1`

. For each **individual** row of the matrix, this row is sorted in non-decreasing order.

1 min readApr 21, 2020

Given a row-sorted binary matrix binaryMatrix, return leftmost column index(0-indexed) with at least a `1`

in it. If such index doesn't exist, return `-1`

.

**You can’t access the Binary Matrix directly.** You may only access the matrix using a `BinaryMatrix`

interface:

`BinaryMatrix.get(x, y)`

returns the element of the matrix at index`(x, y)`

(0-indexed).`BinaryMatrix.dimensions()`

returns a list of 2 elements`[n, m]`

, which means the matrix is`n * m`

.

Submissions making more than `1000`

calls to `BinaryMatrix.get`

will be judged *Wrong Answer*. Also, any solutions that attempt to circumvent the judge will result in disqualification.

For custom testing purposes you’re given the binary matrix `mat`

as input in the following four examples. You will not have access the binary matrix directly.