README_EN.md

1720. Decode XORed Array

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Description

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:

• 2 <= n <= 104
• encoded.length == n - 1
• 0 <= encoded[i] <= 105
• 0 <= first <= 105

Solutions

XOR.

a = b ^ c => a ^ b = b ^ c ^ b => c = a ^ b.

Python3

class Solution:
    def decode(self, encoded: List[int], first: int) -> List[int]:
        res = [first]
        for e in encoded:
            first ^= e
            res.append(first)
        return res

Java

class Solution {
    public int[] decode(int[] encoded, int first) {
        int[] res = new int[encoded.length + 1];
        res[0] = first;
        for (int i = 0; i < encoded.length; ++i) {
            res[i + 1] = res[i] ^ encoded[i];
        }
        return res;
    }
}

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