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Solution.java
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Solution.java
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package ranktransformofarray.hashmap;
import java.util.Arrays;
import java.util.HashMap;
/**
* 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]
*/
class Solution {
/**
* Runtime: 24 ms, faster than 69.62% of Java online submissions for Rank Transform of an Array.
* Memory Usage: 55.4 MB, less than 58.74% of Java online submissions for Rank Transform of an Array.
*
* @param arr
* @return
*/
int[] arrayRankTransform(int[] arr) {
var map = new HashMap<Integer, Integer>();
int[] copy = Arrays.copyOf(arr, arr.length);
Arrays.sort(copy);
// iterate over sorted copy and place element and its corresponding rank in hashmap
for (int n : copy) {
map.putIfAbsent(n, map.size() + 1);
}
// iterate over input array and fetch each element's rank from hashmap
// and place corresponding rank in copy
for (int i = 0; i < arr.length; i++) {
// get rank of element from hashmap
copy[i] = map.get(arr[i]);
}
return copy;
}
}