https://leetcode.com/problems/the-k-weakest-rows-in-a-matrix/

Given a `m * n`

matrix `mat`

of *ones* (representing soldiers) and *zeros* (representing civilians), return the indexes of the `k`

weakest rows in the matrix ordered from the weakest to the strongest.

A row **i** is weaker than row **j**, if the number of soldiers in row **i** is less than the number of soldiers in row **j**, or they have the same number of soldiers but **i** is less than **j**. Soldiers are **always** stand in the frontier of a row, that is, always *ones* may appear first and then *zeros*.

**Example 1:**

**Input:** mat =
[[1,1,0,0,0],
[1,1,1,1,0],
[1,0,0,0,0],
[1,1,0,0,0],
[1,1,1,1,1]],
k = 3
**Output:** [2,0,3]
**Explanation:**
The number of soldiers for each row is:
row 0 -> 2
row 1 -> 4
row 2 -> 1
row 3 -> 2
row 4 -> 5
Rows ordered from the weakest to the strongest are [2,0,3,1,4]