g1701_1800.s1734_decode_xored_permutation.Solution Maven / Gradle / Ivy

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Java-based LeetCode algorithm problem solutions, regularly updated

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package g1701_1800.s1734_decode_xored_permutation;

// #Medium #Array #Bit_Manipulation #2022_04_29_Time_6_ms_(34.52%)_Space_140.9_MB_(66.67%)

/**
 * 1734 - Decode XORed Permutation\.
 *
 * Medium
 *
 * There is an integer array `perm` that is a permutation of the first `n` positive integers, where `n` is always **odd**.
 *
 * It was encoded into another integer array `encoded` of length `n - 1`, such that `encoded[i] = perm[i] XOR perm[i + 1]`. For example, if `perm = [1,3,2]`, then `encoded = [2,1]`.
 *
 * Given the `encoded` array, return _the original array_ `perm`. It is guaranteed that the answer exists and is unique.
 *
 * **Example 1:**
 *
 * **Input:** encoded = [3,1]
 *
 * **Output:** [1,2,3]
 *
 * **Explanation:** If perm = [1,2,3], then encoded = [1 XOR 2,2 XOR 3] = [3,1]
 *
 * **Example 2:**
 *
 * **Input:** encoded = [6,5,4,6]
 *
 * **Output:** [2,4,1,5,3]
 *
 * **Constraints:**
 *
 * *   3 <= n < 10⁵
 * *   `n` is odd.
 * *   `encoded.length == n - 1`
**/
public class Solution {
    public int[] decode(int[] encoded) {
        int[] decoded = new int[encoded.length + 1];
        for (int i = 1; i < encoded.length; i = i + 2) {
            decoded[0] = decoded[0] ^ encoded[i];
            decoded[0] = decoded[0] ^ i;
            decoded[0] = decoded[0] ^ i + 1;
        }
        decoded[0] = decoded[0] ^ decoded.length;
        for (int i = 1; i < decoded.length; i++) {
            decoded[i] = decoded[i - 1] ^ encoded[i - 1];
        }
        return decoded;
    }
}