201. Bitwise AND of Numbers Range

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Given a range [m,n] where 0 <= m <= n <= 2147483647,return the bitwise AND of all numbers in this range,inclusive.

Example 1:

Input: [5,7]
Output: 4

Example 2:

Input: [0,1]
Output: 0

思路：
and 的话必须两个都是1才是1.
先看最后一位。
101
110
111

抹掉，再看下一位
10
11
11
第一位，都是1，一共抹掉2个0，所以 1<<2
1
1
1

 1 class Solution {
 2 public:
 3     int rangeBitwiseAnd(int m,int n) {
 4         int cnt = 0;
 5         while(m!=n){
 6             m>>=1;
 7             n>>=1;
 8             cnt++;
 9         }
10         return n<<cnt;
11         
12     }
13 };