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var smallestSubsequence = function (s) {
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  // Initialize an empty stack to store the result
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  let stack = [];
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  // Iterate through each character in the input string
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  for (let i = 0; i < s.length; i++) {
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    let char = s[i];
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    // If the character is already in the stack, skip it
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    if (stack.indexOf(char) > -1) continue;
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    // Check and pop elements from the stack to maintain lexicographical order
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    while (
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      stack.length > 0 &&
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      stack[stack.length - 1] > char &&
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      s.indexOf(stack[stack.length - 1], i) > i
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    ) {
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      stack.pop();
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    }
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    // Push the current character onto the stack
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    stack.push(char);
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  }
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  // Join the characters in the stack to form the smallest subsequence
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  return stack.join("");
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};