Algorithm: how to find a column in matrix filled with all 1, time complexity O(n)?

Question

I have a matrix which looks like this:

| 1 | 0 | 0 | 1 | 0 |
| 1 | 1 | 0 | 1 | 0 |
| 1 | 0 | 1 | 1 | 0 |
| 1 | 0 | 0 | 1 | 0 |
| 0 | 0 | 0 | 1 | 1 |
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Answer 1

Assuming arbitrary content, you cannot avoid a worst-case of O(n²).^* You have to visit every element in each column that you want to consider, and in the worst-case, you have to consider all columns.

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_{* Also assuming that n is the matrix dimension here, not the total number of elements.}