LeetCode 477: Total Hamming Distance

最新推荐文章于 2021-11-30 23:12:04 发布

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最新推荐文章于 2021-11-30 23:12:04 发布

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原文链接：http://www.cnblogs.com/shuashuashua/p/7469865.html

本文介绍了两种计算哈明距离的方法：一种是通过直接比较两个数的二进制位来计算不同位的数量；另一种是统计每个二进制位上1的数量，并利用组合公式计算贡献值。提供了详细的Java代码实现。

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Note:

1. Very smart way of calculating how many difference from bits: https://en.wikipedia.org/wiki/Hamming_distance#Algorithm_example

2. Another way is counting how many 1s and 0s per bits. Then the contribution of that bit will bt C(1, k) * C(1, n - k).

class Solution {
    public int totalHammingDistance(int[] nums) {
        if (nums.length < 2) {
            return 0;
        }
        
        int result = 0;;
        for (int i = 0; i < nums.length; i++) {
            for (int j = i + 1; j < nums.length; j++) {
                result += getDistance(nums[i], nums[j]);
            }
        }
        return result;
    }
    
    private int getDistance(int a, int b) {
        int c = a ^ b;
        int result = 0;
        while (c != 0) {
            result++;
            c &= c - 1;
        }
        return result;
    }
}

class Solution {
    public int totalHammingDistance(int[] nums) {
        if (nums.length < 2) {
            return 0;
        }
        
        int result = 0;;
        for (int i = 0; i < 32; i++) {
            int ones = 0;
            for (int j = 0; j < nums.length; j++) {
                ones += (nums[j] >> i) & 1;
            }
            result += ones * (nums.length - ones);
        }
        return result;
    }
}