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1331. Rank Transform of an Array 👍

  • Time: $O(n\log n)$
  • Space: $O(n)$
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class Solution {
 public:
  vector<int> arrayRankTransform(vector<int>& arr) {
    vector<int> sortedArr(arr);
    unordered_map<int, int> rank;

    ranges::sort(sortedArr);

    for (const int a : sortedArr)
      if (!rank.contains(a))
        rank[a] = rank.size() + 1;

    for (int& a : arr)
      a = rank[a];

    return arr;
  }
};

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class Solution {
  public int[] arrayRankTransform(int[] arr) {
    int[] sortedArr = arr.clone();
    Map<Integer, Integer> rank = new HashMap<>();

    Arrays.sort(sortedArr);

    for (final int a : sortedArr)
      rank.putIfAbsent(a, rank.size() + 1);

    for (int i = 0; i < arr.length; ++i)
      arr[i] = rank.get(arr[i]);

    return arr;
  }
}

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class Solution:
  def arrayRankTransform(self, arr: list[int]) -> list[int]:
    rank = {}

    for a in sorted(arr):
      if a not in rank:
        rank[a] = len(rank) + 1

    return map(rank.get, arr)