Letter Tile Possibilities LeetCode solution in JavaScript

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//""This solution isn`t the best way but it`s simple""
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var numTilePossibilities = function (tiles) {
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  return search(tiles);
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};
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// this function takes a state and check if it`s valid or !
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// valid state is not null state and unique
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// e.g ["","A","A"]=>is not valid state because is has null state and repeated
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// values by contrast ["A"] is valid state
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// !!state below is to check if state not null
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const isValidState = (state = "", res = []) => !!state && !res.includes(state);
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// this function permutes tiles by backtracking
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const search = (tiles = "", state = "", result = []) => {
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  if (isValidState(state, result))
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    //check if the current state valid
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    result.push(state);
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  //loop through tiles and every time you push letter to state
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  // the remaining tiles will decreased by one
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  /**
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   * ---e.g--
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   * level 1 tiles=AAB state=""
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   * it will loop through the tiles ;
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   * now I am in index 0 push tiles[0] to state now state=A
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   * by making this operation number of option tiles will be
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   * decreased to newTiles="AB"
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   * ...
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   * ..
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   * .
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   * */
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  for (let i = 0; i < tiles.length; i++) {
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    state += tiles[i];
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    const newTiles = tiles.substring(0, i) + tiles.substring(i + 1);
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    search(newTiles, state, result);
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    state = state.slice(0, state.length - 1);
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  }
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  return result.length;
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};