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#1706 - Where Will the Ball Fall
Problem Description
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.
Solution
/**
* @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;
};