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var isRobotBounded = function (instructions) {
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  // north = 0, east = 1, south = 2, west = 3
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  let directions = [
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    [0, 1],
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    [1, 0],
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    [0, -1],
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    [-1, 0],
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  ];
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  // Initial position is in the center
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  let x = 0,
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    y = 0;
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  // facing north
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  let idx = 0;
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  let movements = [...instructions];
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  for (let move of movements) {
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    if (move == "L") idx = (idx + 3) % 4;
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    else if (move == "R") idx = (idx + 1) % 4;
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    else {
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      x += directions[idx][0];
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      y += directions[idx][1];
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    }
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  }
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  // after one cycle:
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  // robot returns into initial position
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  // or robot doesn't face north
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  return (x == 0 && y == 0) || idx != 0;
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};