Given an unsorted array, find the maximum difference between the successive elements in its sorted form.

Try to solve it in linear time/space.

Return 0 if the array contains less than 2 elements.

You may assume all elements in the array are non-negative integers and fit in the 32-bit signed integer range.

public class Solution {
    public int maximumGap(int[] num) {
           if(num == null || num.length < 2) return 0;
        
        int min = num[0], max = num[0];
        int len = num.length;
        for(int i=1; i<len; i++) {
            if(num[i] < min) {
                min = num[i];
            } else if(num[i] > max) {
                max = num[i];
            }
        }
        if(len==2) return max - min;
        int [] min_bs = new int[len+1];
        int [] max_bs = new int[len+1];
        
        for(int i=0; i<len; i++) {
            int x = num[i];
            int k =  (int)(len * (1.0 * (x - min) / (max - min))); //attention! may have overflow problem!
            if(min_bs[k]==0 || x<min_bs[k]) min_bs[k] = x;
            if(max_bs[k]==0 || x>max_bs[k]) max_bs[k] = x;
        }
        
        int maxInter = 0;
        min = max_bs[0];
        for(int i=1; i<len+1; i++) {
            if(min_bs[i] == 0) continue;
            maxInter = Math.max(maxInter, min_bs[i] - min);
            min = max_bs[i];
        }
        return maxInter;
        
    }
}

leetcode 155: Maximum Gap