Force deduction solution summary 1331 array sequence number conversion

Directory links ：

Force buckle programming problem - The solution sums up _ Share + Record -CSDN Blog

GitHub Synchronous question brushing items ：

https://github.com/September26/java-algorithms

Original link ：

Power button

describe ：

Give you an array of integers  arr , Please replace each element in the array with their ordinal number after sorting .

The serial number represents how big an element is . The rules for serial numbers are as follows ：

The serial number from 1 Numbered starting .
The bigger an element is , So the bigger the serial number . If two elements are equal , So they have the same serial number .
The serial number of each number should be as small as possible .
 

Example 1：

Input ：arr = [40,10,20,30]
Output ：[4,1,2,3]
explain ：40 It's the biggest element . 10 It's the smallest element . 20 It's the second smallest number . 30 It's the third smallest number .
Example 2：

Input ：arr = [100,100,100]
Output ：[1,1,1]
explain ： All elements have the same sequence number .
Example 3：

Input ：arr = [37,12,28,9,100,56,80,5,12]
Output ：[5,3,4,2,8,6,7,1,3]
 

Tips ：

0 <= arr.length <= 105
-109 <= arr[i] <= 109

source ： Power button （LeetCode）
link ：https://leetcode.cn/problems/rank-transform-of-an-array
Copyright belongs to the network . For commercial reprint, please contact the official authority , Non-commercial reprint please indicate the source .

Their thinking ：

*  Their thinking ：
*  Copy a arr, by copyArr, Sort it .
*  After sorting, traverse , Generate a map,key Value for each ,value The sequence number to sort .
*  Then traverse arr, from map Find key Replace with the corresponding serial number .

Code ：

public class Solution1331 {

    public int[] arrayRankTransform(int[] arr) {
        int[] copyArr = new int[arr.length];
        System.arraycopy(arr, 0, copyArr, 0, arr.length);
        Arrays.sort(copyArr);

        HashMap<Integer, Integer> map = new HashMap<>();
        Integer lastNum = null;
        for (int i = 0; i < copyArr.length; i++) {
            int value = copyArr[i];
            if (lastNum != null && lastNum == value) {
                continue;
            }
            lastNum = value;
            map.put(value, map.size() + 1);
        }
        for (int i = 0; i < arr.length; i++) {
            int value = arr[i];
            arr[i] = map.get(value);
        }
        return arr;
    }
}