1706-where-will-the-ball-fall.js

/**
 * 1706. Where Will the Ball Fall
 * https://leetcode.com/problems/where-will-the-ball-fall/
 * Difficulty: 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.
 */

/**
 * @param {number[][]} grid
 * @return {number[]}
 */
var findBall = function(grid) {
  const m = grid.length;
  const n = grid[0].length;
  const result = new Array(n);

  for (let col = 0; col < n; col++) {
    let currentCol = col;
    let row = 0;

    while (row < m) {
      const nextCol = currentCol + grid[row][currentCol];

      if (nextCol < 0 || nextCol >= n || grid[row][currentCol] !== grid[row][nextCol]) {
        currentCol = -1;
        break;
      }

      currentCol = nextCol;
      row++;
    }

    result[col] = currentCol;
  }

  return result;
};