338. Counting Bits && 191. Number of 1 Bits

Posted 2020-08-01 蜃利的阴影下

Given a non negative integer number num. For every numbers i in the range 0 ≤ i ≤ num calculate the number of 1‘s in their binary representation and return them as an array.

Example:
For num = 5 you should return [0,1,1,2,1,2].

Follow up:

• It is very easy to come up with a solution with run time O(n*sizeof(integer)). But can you do it in linear time O(n) /possibly in a single pass?
• Space complexity should be O(n).
• Can you do it like a boss? Do it without using any builtin function like __builtin_popcount in c++ or in any other language.

 

Hint:

1. You should make use of what you have produced already.
2. Divide the numbers in ranges like [2-3], [4-7], [8-15] and so on. And try to generate new range from previous.
3. Or does the odd/even status of the number help you in calculating the number of 1s?

 

Hide Tags

 Dynamic Programming Bit Manipulation

Hide Similar Problems

 (E) Number of 1 Bits

 

public class Solution {
    public int[] countBits(int num) {
        int[] ret = new int[num+1];
        // f(i) = f(i/2) + i%2.
        for(int i = 1; i<=num; ++i)
            ret[i] = ret[i/2]+i%2;
        return ret;
    }
}

 

191. Number of 1 Bits

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.

Hide Tags

 Bit Manipulation

Hide Similar Problems

 (E) Reverse Bits (E) Power of Two (M) Counting Bits

 

 

The signed right shift operator ">>" shifts a bit pattern to the right.

The unsigned right shift operator ">>>" shifts a zero into the leftmost position, while the leftmost position after ">>" depends on sign extension.

e.g.

System.out.println(-1 >> 1);   //-1
System.out.println(-1 >> 31);  //-1
System.out.println(-1 >>> 29); //7
System.out.println(-1 >>> 30); //3
System.out.println(-1 >>> 31); //1
System.out.println(-1 >>> 32); //-1,          <=> -1 >>> 0
System.out.println(-1 >>> 33); //2147483647,  <=> -1 >>> 1

int n = -15;
System.out.println(Integer.toBinaryString(n));//11111111111111111111111111110001
int m = n >> 1;
System.out.println(m);//-8
System.out.println(n / 2);//-7
System.out.println(Integer.toBinaryString(m));//11111111111111111111111111111000

　

 

Bit Operators:

http://stackoverflow.com/questions/15457893/java-right-shift-on-negative-number

https://docs.oracle.com/javase/tutorial/java/nutsandbolts/op3.html

 

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