#1293 - Shortest Path in a Grid with Obstacles Elimination

Hard • View on LeetCode • View on GitHub

Problem Description

You are given an m x n integer matrix grid where each cell is either 0 (empty) or 1 (obstacle).

You can move up, down, left, or right from and to an empty cell in one step.

Return the minimum number of steps to walk from the upper left corner (0, 0) to the lower right corner (m - 1, n - 1) given that you can eliminate at most k obstacles. If it is not possible to find such walk return -1.

Solution

function shortestPath(grid, k) {
  const rows = grid.length;
  const cols = grid[0].length;
  if (rows === 1 && cols === 1) return 0;

  let steps = 1;
  let queue = [[0, 0, k]];
  const visited = Array.from({ length: rows }, () => new Int16Array(cols).fill(-1));
  const directions = [0, -1, 0, 1, 0];

  while (queue.length) {
    const nextLevel = [];
    for (const [row, col, obstaclesLeft] of queue) {
      for (let i = 0; i < 4; i++) {
        const newRow = row + directions[i];
        const newCol = col + directions[i + 1];

        if (newRow < 0 || newRow === rows || newCol < 0
            || newCol === cols || visited[newRow][newCol] >= obstaclesLeft) continue;

        if (newRow === rows - 1 && newCol === cols - 1) return steps;

        const remainingObstacles = grid[newRow][newCol] ? obstaclesLeft - 1 : obstaclesLeft;
        visited[newRow][newCol] = remainingObstacles;
        nextLevel.push([newRow, newCol, remainingObstacles]);
      }
    }
    steps++;
    queue = nextLevel;
  }

  return -1;
}