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coding_interviews/leetcode/medium/find-the-original-array-of-prefix-xor/README.md

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+# Find The Original Array of Prefix Xor
+
+[Problem link](https://leetcode.com/problems/find-the-original-array-of-prefix-xor)
+
+- If you want `5 ^ ? = 2`, you can do a reverse xor using `5 ^ 2 = ?`, which in this case `? = 7`
+- If you want to do consecutive XOR operations like `5 ^ 7 ^ 2 ^ 3 ^ 2`, you can replace that with the previous `pref` item
+  - e.g. `5 ^ 7 ^ ? = 0.`, you want to find `?`
+  - so you need to do `5 ^ 7 ^ 0 = ?` but at that point, if you don't store the previous result, you don't have `5 ^ 7`
+  - but you can get this calculation from the previous `pref` item because it can replace `5 ^ 7`, in this case, it is `2`
+- Runtime complexity: O(N), where N is prev.length