leetcode

commit f035e4f04939219d5979f67d9e36b307a60d15fb
parent 3ae87fe80a3a60df750acefceff38c4ab09a9a30
Author: Jack Sangdahl <jack@pngu.org>
Date:   Fri, 15 Aug 2025 08:33:19 +0200

342. power of four

Diffstat:
M
power_of_four.c
 | 
14
++------------
M
power_of_four.py
 | 
2
+-

2 files changed, 3 insertions(+), 13 deletions(-)
diff --git a/power_of_four.c b/power_of_four.c
@@ -1,6 +1,5 @@
 // 342. Power of Four
-#include <stdbool.h>
-#include <stdio.h>
+#include "leetcode.h"
 
 /*
  * given an integer 'n', return 'true' if it is a power of four, otherwise,
@@ -9,16 +8,7 @@
  */
 
 bool isPowerOfFour(int n) {
-  int ans = 0, pos = 1, ones = 0;
-  while (n) {
-    if (n & 1) { // if 'n' is even...
-      ans++;
-      ones = pos;
-    }
-    n >>= 1; // 'n' / 2
-    pos++;
-  }
-  return ans == 1 && ones & 1;
+  return n > 0 && __builtin_popcount((unsigned)n) == 1 && !((n - 1) % 3);
 }
 
 int main() {
diff --git a/power_of_four.py b/power_of_four.py
@@ -9,7 +9,7 @@ return 'false'. an integer 'n' is a power of four if there exists an integer
 
 class Solution(object):
     def isPowerOfFour(self, n):
-        return n != 0 and n & (n - 1) == 0 and n & 1431655765 == n
+        return n > 0 and n.bit_count() == 1 and (n - 1) % 3 == 0
 
 
 if __name__ == "__main__":