LeetCode 1486. XOR Operation in an Array

Posted on Edited on In 
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class Solution {
public:
    int xorOperation(int n, int start) {
        int pre = start, ans = start;
        for (int i = 1 ; i < n; ++i) {
            pre += 2;
            ans ^= pre;
        }
        return ans;
    }
};
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class Solution {
public:
    int sumXor(int x) {
        if (x % 4 == 0) return x;
        if (x % 4 == 1) return 1;
        if (x % 4 == 2) return x + 1;
        return 0;
    }
    int xorOperation(int n, int start) {
        int s = start >> 1, e = n & start & 1;
        int ret = sumXor(s - 1) ^ sumXor(s + n - 1);
        return ret << 1 | e;
    }
};