Simulate pouring water onto terrain

Problem Statement

You are given a 2D grid of non-negative integers terrain, where terrain[i][j] represents the height of the ground at coordinate (i, j). You are also given a coordinate (start_row, start_col) where a unit of water is poured.

Water flows according to these rules:

1. Water at (r, c) will flow to an adjacent cell (up, down, left, or right) that has a strictly lower height than the current cell.
2. If multiple adjacent cells are strictly lower, the water moves to the cell with the minimum height. If there is still a tie, the water moves to the cell that appears first in the order: (r+1, c), (r, c+1), (r-1, c), (r, c-1).
3. If no adjacent cell is strictly lower, the water stays at (r, c) and pools there, increasing the height of the terrain at (r, c) by 1.
4. Water flows off the grid if it reaches a boundary cell and its next move would be outside the (0, 0) to (rows-1, cols-1) bounds.

Implement the function simulate_water(terrain, start_row, start_col) which returns the updated terrain grid after one unit of water has finished settling.

Constraints

• terrain is an N x M grid (1 <= N, M <= 50).
• terrain[i][j] is between 0 and 1000.

Example 1

Input: terrain = [[5, 4, 5], [4, 3, 4], [5, 4, 5]], start = (0, 0) Output: [[5, 4, 5], [4, 4, 4], [5, 4, 5]] Explanation: Water starts at (0,0), flows to (0,1) (height 4), then to (1,1) (height 3), then gets stuck because all neighbors of (1,1) are height 4, so it adds 1 to (1,1).