Minimum Cost to Make at Least One Valid Path in a Grid LeetCode solution in JavaScript

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var minCost = function (grid) {
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  const n = grid.length;
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  const m = grid[0].length;
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  const dns = [
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    [0, 0], // unused, just put here to make reading signs easier
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    [1, 0],
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    [-1, 0],
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    [0, 1],
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    [0, -1],
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  ];
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  const visited = new Set();
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  const q = new MinPriorityQueue();
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  q.enqueue([0, 0], 0);
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  while (q.size()) {
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    const { element, priority: changes } = q.dequeue();
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    const [x, y] = element;
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    if (x === m - 1 && y === n - 1) {
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      return changes;
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    }
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    const key = x + y * m;
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    if (visited.has(key)) continue;
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    visited.add(key);
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    //calculate the direction of the sign and then use it to determine if a change was made whilst pathfinding
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    const sign = grid[y][x];
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    const sx = dns[sign][0] + x;
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    const sy = dns[sign][1] + y;
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    for (let i = 1; i < 5; ++i) {
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      const nx = dns[i][0] + x;
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      const ny = dns[i][1] + y;
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      if (grid[ny]?.[nx] && !visited.has(ny * m + nx)) {
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        const nextChange = sx === nx && sy === ny ? changes : changes + 1;
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        q.enqueue([nx, ny], nextChange);
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      }
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    }
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  }
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};