1720. Decode XORed Array

package LeetCode_1720

/**
 * 1720. Decode XORed Array
 * https://leetcode.com/problems/decode-xored-array/
 * There is a hidden integer array arr that consists of n non-negative integers.
It was encoded into another integer array encoded of length n - 1, such that encoded[i] = arr[i] XOR arr[i + 1].
For example, if arr = [1,0,2,1], then encoded = [1,2,3].
You are given the encoded array. You are also given an integer first, that is the first element of arr, i.e. arr[0].
Return the original array arr. It can be proved that the answer exists and is unique.

Example 1:
Input: encoded = [1,2,3], first = 1
Output: [1,0,2,1]
Explanation: If arr = [1,0,2,1], then first = 1 and encoded = [1 XOR 0, 0 XOR 2, 2 XOR 1] = [1,2,3]

Example 2:
Input: encoded = [6,2,7,3], first = 4
Output: [4,2,0,7,4]

Constraints:
1. 2 <= n <= 104
2. encoded.length == n - 1
3. 0 <= encoded[i] <= 105
4. 0 <= first <= 105
 * */
class Solution {
    /*
    * Solution: XOR the same number twice, all operations on this number will be cancel：a xor b xor a = b;
    * because encoded[i] = result[i] xor result[i+1], 
    * so we add: encoded[i] xor result[i+1] in both side =>
    * encoded[i] xor encoded[i] xor result[i+1] = result[i] xor result[i+1] xor encoded[i] xor result[i+1], 
    * then get:
    * result[i+1]  = result[i] xor encoded[i];
    * Time:O(n), Space:O(1)
    * */
    fun decode(encoded: IntArray, first: Int): IntArray {
        val result = IntArray(encoded.size + 1)
        result[0] = first
        for (i in encoded.indices) {
            result[i + 1] = encoded[i].xor(result[i])
        }
        return result
    }
}