LeetCode 1122. Relative Sort Array



Given two arrays arr1 and arr2, the elements of arr2 are distinct, and all elements in arr2 are also in arr1.

Sort the elements of arr1 such that the relative ordering of items in arr1 are the same as in arr2.  Elements that don’t appear in arr2 should be placed at the end of arr1 in ascending order.

Example 1:

Input: arr1 = [2,3,1,3,2,4,6,7,9,2,19], arr2 = [2,1,4,3,9,6]
Output: [2,2,2,1,4,3,3,9,6,7,19]


  • 1 <= arr1.length, arr2.length <= 1000
  • 0 <= arr1[i], arr2[i] <= 1000
  • All the elements of arr2 are distinct.
  • Each arr2[i] is in arr1.


Using the arr2 order to add the number of elements with the number of occurrences in arr1.

Python Solution

class Solution:
    def relativeSortArray(self, arr1: List[int], arr2: List[int]) -> List[int]:
        results = []
        counter = {}
        for num in arr1:
            counter[num] = counter.get(num, 0) + 1
        for num in arr2:           
            for i in range(counter[num]):

        arr2_set = set(arr2)                
        for num in sorted(arr1):    
            if num not in arr2_set:
        return results
  • Time Complexity: O(N).
  • Space Complexity: O(N).

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