【LeetCode從零單排】No 191.Number of 1 Bits(考察位運算)

李博Garvin發表於2015-03-13
LeetCode

題目

Write a function that takes an unsigned integer and returns the number of ’1' bits it has (also known as the Hamming weight).

For example, the 32-bit integer ’11' has binary representation 00000000000000000000000000001011, so the function should return 3.

Credits:
Special thanks to @ts for adding this problem and creating all test cases.


程式碼

1.遞迴運算，雖然leet不通過，因為時間原因
public class Solution {
    // you need to treat n as an unsigned value
    public static int hammingWeight(int n) {
       if(n==0) return 0;
       if(n==1) return 1;
       int total=1;
       int index=1;
       while(n-total*2>=0){
           total=total*2;
       }
       n=n-total;
       index=index+hammingWeight(n);
       return index;
  }


2.用位運算方法

public class Solution {
    // you need to treat n as an unsigned value
    public int hammingWeight(int n) {
     if(n==0) return 0;
     int i=0;
     while(n!=0){
         n=n & (n-1);
         i++;
     }
     return i;
  }
}




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