2433. Find The Original Array of Prefix Xor
Description
You are given an integer array pref
of size n
. Find and return the array arr
of size n
that satisfies:
pref[i] = arr[0] ^ arr[1] ^ ... ^ arr[i]
.
Note that ^
denotes the bitwise-xor operation.
It can be proven that the answer is unique.
Example 1:
Input: pref = [5,2,0,3,1] Output: [5,7,2,3,2] Explanation: From the array [5,7,2,3,2] we have the following: - pref[0] = 5. - pref[1] = 5 ^ 7 = 2. - pref[2] = 5 ^ 7 ^ 2 = 0. - pref[3] = 5 ^ 7 ^ 2 ^ 3 = 3. - pref[4] = 5 ^ 7 ^ 2 ^ 3 ^ 2 = 1.
Example 2:
Input: pref = [13] Output: [13] Explanation: We have pref[0] = arr[0] = 13.
Constraints:
1 <= pref.length <= 105
0 <= pref[i] <= 106
Solutions
Solution 1: Bit Manipulation
According to the problem statement, we have equation one:
$$ pref[i]=arr[0] \oplus arr[1] \oplus \cdots \oplus arr[i] $$
So, we also have equation two:
$$ pref[i-1]=arr[0] \oplus arr[1] \oplus \cdots \oplus arr[i-1] $$
We perform a bitwise XOR operation on equations one and two, and get:
$$ pref[i] \oplus pref[i-1]=arr[i] $$
That is, each item in the answer array is obtained by performing a bitwise XOR operation on the adjacent two items in the prefix XOR array.
The time complexity is $O(n)$, where $n$ is the length of the prefix XOR array. Ignoring the space consumption of the answer, the space complexity is $O(1)$.
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