# 191. Number of 1 Bits(Solution || Leetcode easy || Java)

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

**Note:**

- Note that in some languages, such as Java, there is no unsigned integer type. In this case, the input will be given as a signed integer type. It should not affect your implementation, as the integer’s internal binary representation is the same, whether it is signed or unsigned.
- In Java, the compiler represents the signed integers using 2’s complement notation. Therefore, in
**Example 3**, the input represents the signed integer.`-3`

.

**Example 1:**

`Input: n = 00000000000000000000000000001011`

Output: 3

Explanation: The input binary string 00000000000000000000000000001011 has a total of three '1' bits.

**Example 2:**

`Input: n = 00000000000000000000000010000000`

Output: 1

Explanation: The input binary string 00000000000000000000000010000000 has a total of one '1' bit.

**Example 3:**

`Input: n = 11111111111111111111111111111101`

Output: 31

Explanation: The input binary string 11111111111111111111111111111101 has a total of thirty one '1' bits.

**Constraints:**

- The input must be a
**binary string**of length`32`

.

**Follow up:** If this function is called many times, how would you optimize it?

# SOLUTION:

`public class Solution {`

// you need to treat n as an unsigned value

public int hammingWeight(int n) {

//start a counter to count number of 1 bits

int count = 0;

//as the input is of length 32 so, run the loop 32 times

for(int i = 0; i < 32; i++){

int k = n & 1;

//if the last bit is equal to 1 increase the counter

if(k == 1){

count++;

}

//as we have checked last bit so, right shift n

n = n >> 1;

}

return count;

}

}

Runtime1 ms

Beats

77.82%

Memory41.1 MB

Beats

50.58%

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