1331. Rank Transform of an Array(Solution || Leetcode easy || Java)

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

SOLUTION:

class Solution {
    public int[] arrayRankTransform(int[] arr) {
        //if the length of array is 0 return arr as it is
        if(arr.length == 0){
            return arr;
        }
        
        //Create array to store the elements of original array
         int[] temp = new int[arr.length];

        //add elements of original array in our new array
        for(int i = 0; i < arr.length; i++){
            temp[i] = arr[i];
        }
    
        //sort the temporary array
        Arrays.sort(temp);
        
        //create an array to store rank of the temporary array
        int[] ranks = new int[arr.length];
        ranks[0] = 1;
        
        int r = 1;
        
        //Assign ranks to elements 
        for(int i = 1; i < arr.length; i++){
            if(temp[i] != temp[i-1]){
                r++;
            } 
            ranks[i] = r;
        }
        
        //We are going to search the element of original array
      // into our temporary array and after finding the element 
      //in our temporary array we will give the rank to that element
     // from our rank array
        for(int i = 0; i < arr.length; i++){
            int start = 0;
            int end = temp.length - 1;
            
            while(start <= end){
                int mid = start + (end - start)/2;
                
                if(temp[mid] == arr[i]){
                    arr[i] = ranks[mid];
                    break;
                }
                else if(temp[mid] > arr[i]){
                    end = mid - 1;
                }
                else{
                    start = mid + 1;
                }
            }
        }
        
        return arr;
    }
}

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