LintCode "Maximum Gap"

Bucketing! A lot of details to take care.

struct Bucket
{
    Bucket() :l(-1), r(-1), bValid(false){};
int l, r;
    bool bValid;
};

class Solution {
public:
    /**
    * @param nums: a vector of integers
    * @return: the maximum difference
    */
    int maximumGap(vector<int> nums)
    {
        //  Remove duplicates
        unordered_set<int> hs(nums.begin(), nums.end());
        nums.assign(hs.begin(), hs.end());
        //
        size_t n = nums.size();
        if (n < 2) return 0;
        
        long long mn = *min_element(nums.begin(), nums.end());
        long long mx = *max_element(nums.begin(), nums.end());
        if (mn == mx) return 0;

        //  Set up buckets
        vector<Bucket> bk(n);
        long long interval = (mx - mn + 1) / (long long)(n - 1);
for (auto v : nums)
        {
            int binx = (v - mn) / interval;
            bk[binx].l = (!bk[binx].bValid) ? v : min(bk[binx].l, v);
            bk[binx].r = (!bk[binx].bValid) ? v : max(bk[binx].r, v);
            bk[binx].bValid = true;
        }

        //  Go check bucket by bucket
        int i = 0, ret = 0;
        while (i < bk.size())
        {
            if (bk[i].bValid)
            {
                int wi = bk[i].r - bk[i].l, wo = 0;
                
                int j = i + 1;
                while (j < bk.size() && !bk[j].bValid) j++;
                if (j < bk.size())
                    wo = bk[j].l - bk[i].r;
                
                ret = max(ret, max(wi, wo));
                i = j;
            }
            else
                i++;
        }
        return ret;
    }
};