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Update Count of Smaller Numbers After Self.cpp #620

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56 changes: 56 additions & 0 deletions Count of Smaller Numbers After Self.cpp
Original file line number Diff line number Diff line change
@@ -1,4 +1,6 @@


/* Approach 1: Using merge-sort technique */
void merge(vector<pair<int ,int > > &v,int l,int mid,int r,vector<int > &ans){
int i=l,j=mid,k=0;
vector<pair<int ,int > > temp(r-l+1);
Expand Down Expand Up @@ -46,3 +48,57 @@ class Solution {
return ans;
}
};



/* Approach 2: Using Policy Based Data Structure technique */
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#include <bits/stdc++.h>

using namespace __gnu_pbds;
using namespace std;


typedef tree<int, null_type, less_equal<int>, rb_tree_tag, tree_order_statistics_node_update> pbds;


class Solution {
public:

void myerase(pbds &t, int v){

int rank = t.order_of_key(v);
pbds::iterator it = t.find_by_order(rank);
t.erase(it);
}
vector<int> countSmaller(vector<int>& nums) {

int n = nums.size();
pbds st;
for(int i = n - 1 ; i >= 0 ; i--)
{
st.insert(nums[i]);
}

vector<int> count(n);
for(int i = 0 ; i < n ; i++)
{

myerase(st, nums[i]);

auto it = st.upper_bound(nums[i]);
if(it == st.end())
count[i] = st.size();

else
count[i] = st.order_of_key(*it);

if(count[i] < 0)
count[i] = 0;
}

return count;

}
};