1331. 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

class Solution {
    public int[] arrayRankTransform(int[] arr) {
        Map<Integer, List<Integer>> map = new TreeMap();
        int rank = 1;
        
        for(int i = 0; i < arr.length; i++){
            map.putIfAbsent(arr[i], new ArrayList());
            map.get(arr[i]).add(i);
        }
        for(Map.Entry<Integer, List<Integer>> entry: map.entrySet()){
            List<Integer> cur = entry.getValue();
            for(int i: cur) arr[i] = rank;
            rank++;
        }
        return arr;
    }
}

虽然是个easy的题，但感觉还挺有意思

先用treemap把key从小到大排序，同时value用数组记录key的index

然后遍历每个key的value，然后把rank放入数组，rank++