leetcode 321. Create Maximum Number

Given two arrays of length 

m

 and 

n

 with
digits 

0-9

 representing two numbers. Create the maximum number of length 

k
<= m + n

 from digits of the two. The relative order of the digits from the same array must be preserved. Return an array of the 

k

 digits.
You should try to optimize your time and space complexity.

Example 1:

nums1 = 

[3, 4, 6, 5]

nums2 = 

[9, 1, 2, 5, 8, 3]

k = 

5

return 

[9, 8, 6, 5, 3]

Example 2:

nums1 = 

[6, 7]

nums2 = 

[6, 0, 4]

k = 

5

return 

[6, 7, 6, 0, 4]

Example 3:

nums1 = 

[3, 9]

nums2 = 

[8, 9]

k = 

3

return 

[9, 8, 9]

看到题先打个标签，贪心问题，大致思路有了，剩下就是程序设计的细节。

这题还算难点的。程序设计时往往需要考虑特例情况，在这一题中就要考虑某次可以从nums1和nums2里取出的最大的数相等的情况该怎么办，这时你如果死揪着这个不放就会陷入一个黑洞——如果往下算一层还是相等怎么办？这样程序写起来就会很复杂，而且不清晰，甚至根本写不出来。这时你就要换一个思路了。程序员要做的应该是简单的事，复杂的事嘛就交给计算机好了。这话说起来容易，其实要做到挺不容易，慢慢体会吧。

回到这个问题，非要在这次就得到一个唯一的答案吗？不必的。相等的话就都留下吧，留给下一次处理，不要妄想一次就把所有问题都解决，每次解决一点，每次都往正确解靠近就行。

class Solution {
public:
int do_once(vector<int>&nums1,vector<int>&nums2,vector<pair<int, int>>&candi, int k,set<pair<int,int>>&hist)
{
vector<pair<int, int>>newcandi;
int maxret = 0;
for (int i = 0; i < candi.size(); i++)
{
int choose1(-1), choose2(-1);
int ptr1(0), ptr2(0);
if (nums1.size()-candi[i].first + nums2.size()-candi[i].second == k)
{
if (candi[i].first==nums1.size() || candi[i].second==nums2.size())
{
if (candi[i].first == nums1.size())
{
if (nums2[candi[i].second] >= maxret)
{
if (nums2[candi[i].second] > maxret)
{
maxret = nums2[candi[i].second];
newcandi.clear();
}
int aa = candi[i].second+1;
if (hist.find(pair<int, int>(candi[i].first,aa)) == hist.end())
{
newcandi.push_back(pair<int, int>( candi[i].first,aa));
hist.insert(pair<int, int>(candi[i].first,aa));
}
}
}
if (candi[i].second==nums2.size())
{
if (nums1[candi[i].first] >= maxret)
{
if (nums1[candi[i].first] > maxret)
{
maxret = nums1[candi[i].first];
newcandi.clear();
}
int aa = candi[i].first+1;
if (hist.find(pair<int, int>(aa, candi[i].second)) == hist.end())
{
newcandi.push_back(pair<int, int>(aa, candi[i].second));
hist.insert(pair<int, int>(aa, candi[i].second));
}
}
}
}
else
{
int gt = nums1[candi[i].first] > nums2[candi[i].second] ? nums1[candi[i].first] : nums2[candi[i].second];
if (gt >= maxret)
{
if (gt > maxret)
{
newcandi.clear();
maxret = gt;
}
if (nums1[candi[i].first] > nums2[candi[i].second])
{
int aa = candi[i].first+1;
if (hist.find(pair<int, int>(aa, candi[i].second)) == hist.end())
{
newcandi.push_back(pair<int, int>(aa, candi[i].second));
hist.insert(pair<int, int>(aa, candi[i].second));
}
}
else if (nums1[candi[i].first] < nums2[candi[i].second])
{
int aa = candi[i].second+1;
if (hist.find(pair<int, int>( candi[i].first,aa)) == hist.end())
{
newcandi.push_back(pair<int, int>(candi[i].first,aa));
hist.insert(pair<int, int>( candi[i].first,aa));
}
}
else
{
int aa = candi[i].second+1;
if (hist.find(pair<int, int>(candi[i].first,aa)) == hist.end())
{
newcandi.push_back(pair<int, int>( candi[i].first,aa));
hist.insert(pair<int, int>( candi[i].first,aa));
}

int bb = candi[i].first+1;
if (hist.find(pair<int, int>(bb, candi[i].second)) == hist.end())
{
newcandi.push_back(pair<int, int>(bb, candi[i].second));
hist.insert(pair<int, int>(bb, candi[i].second));
}
}
}
}
}
else
{
int j1max = -1;
int a1= nums1.size()-candi[i].first;
int a2= nums2.size()-candi[i].second;
j1max = a1 + a2 - k <= a1 - 1 ? a1 + a2 - k + candi[i].first : a1 - 1 + candi[i].first;
for (int j = candi[i].first; j <= j1max; j++)
if (nums1[j] > choose1)
{
choose1 =nums1[j];
ptr1 = j;
}
int j2max = -1;
j2max = a1 + a2 - k <= a2 - 1 ? a1 + a2 - k + candi[i].second : a2 - 1 + candi[i].second;
for (int j = candi[i].second; j <= j2max; j++)
if (nums2[j] > choose2)
{
choose2 = nums2[j];
ptr2 = j;
}
int gt = choose1 > choose2 ? choose1 : choose2;
if (gt >= maxret)
{
if (gt > maxret)
{
newcandi.clear();
maxret = gt;
}
if (choose1 > choose2)
{
int aa = ptr1+1;
if (hist.find(pair<int, int>(aa, candi[i].second)) == hist.end())
{
newcandi.push_back(pair<int, int>(aa, candi[i].second));
hist.insert(pair<int, int>(aa, candi[i].second));
}
}
else if (choose1 < choose2)
{
int aa = ptr2+1;
if (hist.find(pair<int, int>( candi[i].first,aa)) == hist.end())
{
newcandi.push_back(pair<int, int>(candi[i].first,aa));
hist.insert(pair<int, int>( candi[i].first,aa));
}
}
else
{
int aa = ptr2+1;
if (hist.find(pair<int, int>(candi[i].first,aa)) == hist.end())
{
newcandi.push_back(pair<int, int>(candi[i].first,aa));
hist.insert(pair<int, int>(candi[i].first,aa));
}

int bb = ptr1+1;
if (hist.find(pair<int, int>(bb, candi[i].second)) == hist.end())
{
newcandi.push_back(pair<int, int>(bb, candi[i].second));
hist.insert(pair<int, int>(bb, candi[i].second));
}
}
}
}
}
candi = newcandi;
return maxret;
}
vector<int> maxNumber(vector<int>& nums1, vector<int>& nums2, int k)
{
vector<int>re;
vector<pair<int, int>>candi;
candi.push_back(pair<int, int>(0, 0));
set<pair<int, int>>hist;
while (k > 0)
{
re.push_back(do_once(nums1,nums2,candi, k,hist));
k--;
}
return re;
}
};

accepted