Create xor-operation-in-an-array.cpp

Author: kamyu104

C++/xor-operation-in-an-array.cpp

@@ -0,0 +1,35 @@
+// Time:  O(1)
+// Space: O(1)
+
+class Solution {
+public:
+    int xorOperation(int n, int start) {
+        return int(n % 2 && start % 2) + 2 * xorNums(n, start / 2);
+    }
+
+private:    
+    int xorNums(int n, int start) {
+        return (start % 2)
+               ? start ^ xorNumsBeginEven(n - 1, start + 1)
+               : xorNumsBeginEven(n, start);
+    }
+    
+    int xorNumsBeginEven(int n, int start) {
+        assert(start % 2 == 0);
+        // 2*i ^ (2*i+1) = 1
+        return ((n / 2) % 2) ^ ((n % 2) ? (start + n - 1) : 0);
+    }
+};
+
+// Time:  O(n)
+// Space: O(1)
+class Solution2 {
+public:
+    int xorOperation(int n, int start) {
+        int result = 0;
+        for (int i = start + 2 * n - 2; i >= start; i -= 2) {
+            result ^= i;
+        }
+        return result;
+    }
+};