1122.RelativeSortArray.cs

// 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 do not 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]
// Example 2:
// Input: arr1 = [28,6,22,8,44,17], arr2 = [22,28,8,6]
// Output: [22,28,8,6,17,44]
 

// Constraints:
// 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 frequency Array
public class Solution {
    public int[] RelativeSortArray(int[] arr1, int[] arr2) {
        int max = arr1.Max();
        int[] freqArr = new int[max+1];
        foreach(var num in arr1)
            freqArr[num]++;
        int i = 0;
        foreach(var num in arr2){
            while(freqArr[num] > 0){
                arr1[i++] = num;
                freqArr[num]--;
            }
        }
        for(int j = 0; j<freqArr.Length; j++){
            while(freqArr[j]>0){
                arr1[i++] = j;
                freqArr[j]--;
            }
        }
        return arr1;
    }
}

//Approch 2 Using Hashmap
public class Solution {
    public int[] RelativeSortArray(int[] arr1, int[] arr2) {
        Dictionary<int, int> freq = new Dictionary<int, int>();
        foreach (var num in arr1) {
            if (freq.ContainsKey(num)) {
                freq[num]++;
            } else {
                freq[num] = 1;
            }
        }

        int i = 0;
        foreach (var num in arr2) {
            if (freq.ContainsKey(num)) {
                while (freq[num] > 0) {
                    arr1[i++] = num;
                    freq[num]--;
                }
                freq.Remove(num);
            }
        }

        List<int> remain = freq.SelectMany(kv => Enumerable.Repeat(kv.Key, kv.Value)).OrderBy(x => x).ToList();
        foreach (var num in remain) {
            arr1[i++] = num;
        }

        return arr1;
    }
}