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Java-based LeetCode algorithm problem solutions, regularly updated
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package g1701_1800.s1706_where_will_the_ball_fall;

// #Medium #Array #Dynamic_Programming #Depth_First_Search #Matrix #Simulation
// #Level_2_Day_1_Implementation/Simulation #2022_04_24_Time_2_ms_(64.55%)_Space_54.5_MB_(25.38%)

/**
 * 1706 - Where Will the Ball Fall\.
 *
 * 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_ i^th _column at the top, or `-1` _if the ball gets stuck in the box_._
 *
 * **Example 1:**
 *
 * **![](https://assets.leetcode.com/uploads/2019/09/26/ball.jpg)**
 *
 * **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`.
**/
@SuppressWarnings("java:S135")
public class Solution {
    public int[] findBall(int[][] grid) {
        int m = grid.length;
        int n = grid[0].length;
        int[] res = new int[n];
        for (int j = 0; j < n; j++) {
            int currentJ = j;
            int currentI = 0;
            while (currentJ < n && currentI < m) {
                if (grid[currentI][currentJ] == 1) {
                    currentJ++;
                    if (currentJ < n && grid[currentI][currentJ] == 1) {
                        currentI++;
                    } else {
                        break;
                    }
                } else {
                    currentJ--;
                    if (currentJ >= 0 && grid[currentI][currentJ] == -1) {
                        currentI++;
                    } else {
                        break;
                    }
                }
            }
            if (currentI == m) {
                res[j] = currentJ;
            } else {
                res[j] = -1;
            }
        }
        return res;
    }
}