Xor-Of-First-N-Natural-Numbers

theSoberSobber · Nov 3, 2024 · 07a9944 · 07a9944
1 parent 9b7be82
commit 07a9944
Showing 1 changed file with 19 additions and 0 deletions.
diff --git a/codes/Xor-Of-First-N-Natural-Numbers.cpp b/codes/Xor-Of-First-N-Natural-Numbers.cpp
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+//Xor of first N Natural Numbers
+//based on the fact that if n%4==3 then xor till n from 1 is 0
+
+auto xorOfFirstN = [&](int n) -> int {
+    // n%4 = 3 => xor = 0
+    int t = n, ans = 0;
+    while(t%4!=3) ans^=t, --t;
+    return ans;
+};
+
+// more explicit version
+int computeXOR(int n) {
+    if (n % 4 == 0) return n;
+    if (n % 4 == 1) return 1;
+    if (n % 4 == 2) return n + 1;
+    return 0;
+}
+
+// source: https://www.geeksforgeeks.org/calculate-xor-1-n/