Fully Passable Rows and Columns in a Grid

Question

## Problem

Given a grid of '0' (passable) and '+' (blocked), return the indices of rows and columns that are entirely passable.

## Example
```
rows/cols with all '0' -> their indices
```

## Constraints
- 1 ≤ m,n ≤ 10^3

## Approach
Row/column scans with boolean flags. Reported Splunk question.