where_will_the_ball_fall.go

package main

// idea: we can simulate the movement of each ball
// if a ball is stuck at some point, then it would be -1
// otherwise, get the final destination column
func findBall(grid [][]int) []int {
	m, n := len(grid), len(grid[0])
	ans := []int{}
	// iterate each column
	for col := 0; col < n; col++ {
		cur_col := col
		// iterate each row
		for cur_row := 0; cur_row < m; cur_row++ {
			// the next column would be the current column + the value of the current cell
			// e.g. column0 + 1 = column 1 (move to the right)
			// e.g. column3 - 1 = column 2 (move to the left)
			next_col := cur_col + grid[cur_row][cur_col]
			// after that we need to check if the ball gets stuck at the same column
			// and there are three cases
			// 1. the ball on the leftmost column and the ball is moving to the left
			// hence, we check `next_col < 0`
			// 2. the ball on the rightmost column and the ball is moving to the right
			// hence, we check `next_col >= n`
			// 3. the ball is stuck at a V shape position
			// e.g. ball 2 and ball 3 in column 2 and column 3 in row 0
			// hence, we check if the if grid[cur_row][cur_col] is different than grid[cur_row][next_col]
			if next_col < 0 || next_col >= n || grid[cur_row][cur_col] != grid[cur_row][next_col] {
				// the ball is stuck at some point, which means it couldn't reach to the end
				// hence, we can set -1 and break here
				cur_col = -1
				break
			}
			// continue the above process with the updated cur_col
			cur_col = next_col
		}
		// the ball reaches to the end,
		// cur_col is the final destination
		ans = append(ans, cur_col)
	}
	return ans
}