# Simple example for the "Java O(n) time O(1) Space" Solution

• The idea is same as https://discuss.leetcode.com/topic/72092/java-o-n-time-o-1-space
Assuming we have an array of five integers `a, b, c, d, e` as follow.
We examine the digits one by one from the last digit.
Count the number of integers whose last digit is 1, assign the value to `ones`

``````    a = 0 0 0 1 0
b = 1 0 0 1 1
c = 0 1 0 0 1
d = 1 0 0 1 0
e = 0 0 0 1 0
↑
ones: b, c
zeros: a, d, e

pairs that make distance are:
b: a, d, e
c: a, d, e

So we have 2 ones and 5 - 2 = 3 zeros
Total distance = 2 * 3
then we move the pointer one position left, i.e. all the numbers right shift by 1 (num >>> 1)
``````

The code is as follows.

``````public int totalHammingDistance(int[] nums) {
int res = 0, len = nums.length;
for(int i = 0; i < 32; i++) { //32 digits in integers
int ones = 0;
for(int j = 0; j < len; j++) {
if((nums[j] & 1) == 1) ones++;
nums[j] = nums[j] >>> 1;
}
res = res + ones * (len - ones);
}
return res;
}
``````

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