LeetCode 1331. Rank Transform of an Array

Description

https://leetcode.com/problems/rank-transform-of-an-array/

Given an array of integers arr, replace each element with its rank.

The rank represents how large the element is. The rank has the following rules:

  • Rank is an integer starting from 1.
  • The larger the element, the larger the rank. If two elements are equal, their rank must be the same.
  • Rank should be as small as possible.

Example 1:

Input: arr = [40,10,20,30]
Output: [4,1,2,3]
Explanation: 40 is the largest element. 10 is the smallest. 20 is the second smallest. 30 is the third smallest.

Example 2:

Input: arr = [100,100,100]
Output: [1,1,1]
Explanation: Same elements share the same rank.

Example 3:

Input: arr = [37,12,28,9,100,56,80,5,12]
Output: [5,3,4,2,8,6,7,1,3]

Constraints:

  • 0 <= arr.length <= 105
  • -109 <= arr[i] <= 109

Explanation

Find and build a map of number’s orders and create a list of orders base on the original list.

Python Solution

class Solution:
    def arrayRankTransform(self, arr: List[int]) -> List[int]:
        
        arr_set = set(arr)
        
        sorted_arr = sorted(list(arr_set))
        
        num_map = {}
        for i, num in enumerate(sorted_arr):
            num_map[num] = i + 1
        
        results = []
        for num in arr:
            results.append(num_map[num])
        
        return results        
        
  • Time Complexity: O(N).
  • Space Complexity: O(N).

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