python C++ bit 計算O(1)時間解Leetcode 201 Bitwise AND of Numbers Range

python C++ bit 計算O(1)時間解Leetcode 201  Bitwise AND of Numbers Range

這就是用x&(x-1)技法。有人會說計算時間是O(log n)，但32-bit整數，無論是迴圈或遞迴頂多32次。如果要熟透bit處理的訣竅，還有更厲害的技法，請進

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python C++ bit calculation O(1) time solution Leetcode 201 Bitwise AND of Numbers Range

This is using the x&(x-1) technique. Some people would say that the calculation time is O(log n), but for 32-bit integers, no matter it is looping or recursing, it can be done at most 32 times.

[codes on Leetcode]https://leetcode.com/problems/bitwise-and-of-numbers-range/solutions/4759874/bitwise-o32-time0ms-beats-100/

[Leetcode playList]https://www.youtube.com/watch?v=WjrWkPysfRM&list=PLYRlUBnWnd5IdDHk2BjqXwesydU17z_xk

[Dynamic Programming Playlist]https://www.youtube.com/watch?v=30yq3fmE6E8&list=PLYRlUBnWnd5K_XYUesV9oc6M9ONXII61T

#pragma GCC optimize("O3", "unroll-loops")
class Solution {
   public:
     int rangeBitwiseAnd(int left, int right) {
       if (left==0 ||countl_zero((unsigned)left)!=countl_zero((unsigned)right)) return 0;
       return left & right & -(1<<(32-countl_zero((unsigned)right-left)));
  }
};