无序数组内相邻两个数的最大差值

/**
 * 求无序数组内相邻两个数的最大差值
 * 可参考文章：
 * https://www.cnblogs.com/xiaomoxian/p/5189782.html
 */

public class BucketSortExtMaxGap {

    public static void main(String[] args) {
        int arr[] = {1, 100, 20, 60, 101};
        System.out.println(getMaxGap(arr));
    }

    private static Integer getMaxGap(int[] arr) {
        if (arr == null || arr.length < 2) {
            return 0;
        }
        int len = arr.length;
        int min = Integer.MAX_VALUE;
        int max = Integer.MIN_VALUE;
        for (int i = 0; i < len; i++) {
            min = Math.min(min, arr[i]);
            max = Math.max(max, arr[i]);
        }
        if (max == min) {
            return 0;
        }

        //初始化3个桶，分别记录 是否为空，最大值，最小值
        boolean[] hasNum = new boolean[len + 1];
        int[] maxs = new int[len + 1];
        int[] mins = new int[len + 1];

        int bid = 0;
        for (int i = 0; i < len; i++) {
            //选择所在的桶
            bid = bucket(arr[i], len, min, max);
            mins[bid] = hasNum[bid] ? Math.min(mins[bid], arr[i]) : arr[i];
            maxs[bid] = hasNum[bid] ? Math.max(maxs[bid], arr[i]) : arr[i];
            hasNum[bid] = true;
        }
        //计算差值
        int res = 0;
        int lastMax = maxs[0];
        int i = 1;
        for (; i <= len; i++) {
            if (hasNum[i]) {
                res = Math.max(res, mins[i] - lastMax);
                lastMax = maxs[i];
            }
        }
        return res;
    }

    /**
     * 确定值所属的桶 ? 这个是怎么算出来的？
     *
     * @param num
     * @param len
     * @param min
     * @param max
     * @return
     */
    public static int bucket(long num, long len, long min, long max) {
        int index = (int) ((num - min) * len / (max - min));
        //System.out.println("index = " + index);
        return index;
    }

}