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

2 min readDec 20, 2022

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


  • 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.


  • The input must be a binary string of length 32.

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


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){

//as we have checked last bit so, right shift n
n = n >> 1;

return count;

Runtime1 ms



Memory41.1 MB



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