class Solution {

int totalSteps(vector<int>& nums)

{

int n = nums.size();

list<int> List;

unordered_map<int,list<int>::iterator>key2iter;

for (int i=0; i<n; i++)

{

List.push_back(i);

key2iter[i] = prev(List.end());

}

queue<int>q;

for (int i=1; i<n; i++)

if (nums[i-1]>nums[i])

q.push(i);

int step = 0;

while (!q.empty())

{

int len = q.size();

unordered_set<int>Set;

while (len--)

{

int i = q.front();

q.pop();

auto iter = key2iter[i];

if (Set.count(i))

Set.erase(i);

if (next(iter)!=List.end())

Set.insert(*next(iter));

List.erase(iter);

}

for (int i: Set)

{

if (key2iter[i]!=List.begin() && nums[*prev(key2iter[i])] > nums[i])

q.push(i);

}

step++;

}

return step;

}

};