Create find-kth-bit-in-nth-binary-string.cpp

Author: kamyu104

C++/find-kth-bit-in-nth-binary-string.cpp

@@ -0,0 +1,20 @@
+// Time:  O(n)
+// Space: O(1)
+
+class Solution {
+public:
+    char findKthBit(int n, int k) {
+        int flip = 0;  // init bit (S1) is 0
+        for (int l = (1 << n) - 1; k > 1; l /= 2) {  // loop from Sn to S1, early return if k == 1
+            if (k == l / 2 + 1) {
+                flip ^= 1;  // hit mid, xor 1
+                break;
+            }
+            if (k > l / 2) {
+                k = l + 1 - k;
+                flip ^= 1;  // right-hand side, invert once
+            }
+        }
+        return '0' + flip;
+    }
+};