bit manipulation

17_Bit-Manipulation/08. Find Kth Bit in Nth Binary String.py

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+# https://leetcode.com/problems/find-kth-bit-in-nth-binary-string/
+
+
+''' 
+# Brute Force Solution
+class Solution:
+    def findKthBit(self, n: int, k: int) -> str:
+
+        def revinv(s):
+            s = list(s)
+            for i in range(len(s)):
+                if s[i] == '0':
+                    s[i] = '1'
+                else:
+                    s[i] = '0'
+            s = ''.join(s)
+            s = s[::-1]
+            return s
+        
+        dp = ['0'] * n
+        dp[0] = '0'
+        for i in range(n):
+            dp[i] = dp[i-1] + '1' + revinv(dp[i-1])
+        
+        return dp[-1][k-1]
+
+# Time: O(n^2)
+# Space: (n)
+''' 
+
+
+# Optimal Solution:
+class Solution:
+    def findKthBit(self, n, k):
+        return str(k / (k & -k) >> 1 & 1 ^ k & 1 ^ 1)