Find in a Grid in C++

Given a grid of integers grid and an integer target, find the first cell equal to target and return its position as a vector of two integers: its row and its column.

A grid is a vector of rows, and each row is a vector of integers. Rows are numbered from 0, top to bottom, and columns from 0, left to right.

"First" means in reading order: the top row from left to right, then the next row, and so on. If no cell is equal to target, return [-1, -1].

Example 1:

Input: grid = [
  [1, 2, 3],
  [4, 5, 6],
  [7, 8, 9]
], target = 6
Output: [1, 2]
Explanation: 6 is in row 1 (the second row) and column 2 (the third column).

Example 2:

Input: grid = [
  [5, 1],
  [1, 5]
], target = 1
Output: [0, 1]
Explanation: 1 appears twice. Reading row by row, the 1 in row 0, column 1 comes before the 1 in row 1, column 0.

Example 3:

Input: grid = [
  [4, 4],
  [4, 4]
], target = 3
Output: [-1, -1]
Explanation: No cell is equal to 3.

Constraints:

• grid has at least 1 row and 1 column, and every row has the same number of values.
• Every value and target is an integer between -1000 and 1000; they can be negative.