WhereWillTheBallFall1706.kt

package medium

/**
 * You have a 2-D grid of size m x n representing a box, and you have n balls. The box is open on the top and bottom sides.

Each cell in the box has a diagonal board spanning two corners of the cell that can redirect a ball to the right or to the left.

A board that redirects the ball to the right spans the top-left corner to the bottom-right corner and is represented in the grid as 1.
A board that redirects the ball to the left spans the top-right corner to the bottom-left corner and is represented in the grid as -1.
We drop one ball at the top of each column of the box. Each ball can get stuck in the box or fall out of the bottom. A ball gets stuck if it hits a "V" shaped pattern between two boards or if a board redirects the ball into either wall of the box.

Return an array answer of size n where answer[i] is the column that the ball falls out of at the bottom after dropping the ball from the ith column at the top, or -1 if the ball gets stuck in the box.



Example 1:



Input: grid = [[1,1,1,-1,-1],[1,1,1,-1,-1],[-1,-1,-1,1,1],[1,1,1,1,-1],[-1,-1,-1,-1,-1]]
Output: [1,-1,-1,-1,-1]
Explanation: This example is shown in the photo.
Ball b0 is dropped at column 0 and falls out of the box at column 1.
Ball b1 is dropped at column 1 and will get stuck in the box between column 2 and 3 and row 1.
Ball b2 is dropped at column 2 and will get stuck on the box between column 2 and 3 and row 0.
Ball b3 is dropped at column 3 and will get stuck on the box between column 2 and 3 and row 0.
Ball b4 is dropped at column 4 and will get stuck on the box between column 2 and 3 and row 1.
Example 2:

Input: grid = [[-1]]
Output: [-1]
Explanation: The ball gets stuck against the left wall.
Example 3:

Input: grid = [[1,1,1,1,1,1],[-1,-1,-1,-1,-1,-1],[1,1,1,1,1,1],[-1,-1,-1,-1,-1,-1]]
Output: [0,1,2,3,4,-1]


Constraints:

m == grid.length
n == grid[i].length
1 <= m, n <= 100
grid[i][j] is 1 or -1.
 */
fun findBall(grid: Array<IntArray>): IntArray {
    val result = IntArray(grid[0].size)
    for(i in grid[0].indices)
    {
        result[i]= findBallDFS(grid,0,i)
    }
    return result
}

fun findBallDFS(grid: Array<IntArray>, row: Int, col: Int): Int {
    // base case when ball arrive to last row
    if (row == grid.size) return col

    val nextColumn = col + grid[row][col]
    if (nextColumn < 0 || nextColumn > grid[0].size - 1 || grid[row][col] != grid[row][nextColumn])
        return -1
    return findBallDFS(grid, row + 1, nextColumn)
}