[LintCode] Create Maximum Number 创建最大数

class Solution {
public:
    /**
     * @param nums1 an integer array of length m with digits 0-9
     * @param nums2 an integer array of length n with digits 0-9
     * @param k an integer and k <= m + n
     * @return an integer array
     */
    vector<int> maxNumber(vector<int>& nums1, vector<int>& nums2, int k) {
        vector<int> res;
        int m = nums1.size(), n = nums2.size();
        for (int i = max(0, k - n); i <= min(k, m); ++i) {
            res = max(res, mergeVec(maxVec(nums1, i), maxVec(nums2, k - i)));
        }
        return res;
    }
    vector<int> maxVec(vector<int> nums, int k) {
        if (k == 0) return {};
        vector<int> res;
        int drop = nums.size() - k;
        for (auto a : nums) {
            while (drop && res.size() && res.back() < a) {
                res.pop_back();
                --drop;
            }
            res.push_back(a);
        }
        res.resize(k);
        return res;
    }
    vector<int> mergeVec(vector<int> nums1, vector<int> nums2) {
        vector<int> res;
        while (nums1.size() + nums2.size()) {
            vector<int> &t = nums1 > nums2 ? nums1 : nums2;
            res.push_back(t[0]);
            t.erase(t.begin());
        }
        return res;
    }
};