given an array, for each element, find out the total number of elements lesser than it, which appear to the right of it

Question

I had previously posted a question, Given an array, find out the next smaller element for each element now, i was trying to know , if there is any way to find out \"given an ar

Answer 1

You can also use binary Index tree

int tree[1000005];
void update(int idx,int val)
{
   while(idx<=1000000)
   {
       tree[idx]+=val;
       idx+=(idx & -idx);
   }
}

int sum(int idx)
{
    int sm=0;
    while(idx>0)
    {
       sm+=tree[idx];
       idx-=(idx & -idx);
    }
    return sm;
}

int main()
{
    int a[]={4,2,1,5,3};
    int s=0,sz=6;
    int b[10];
    b[sz-1]=0;
    for(int i=sz-2;i>=0;i--)
    {
        if(a[i]!=0)
        {
            update(a[i],1);
            b[i]=sum(a[i]-1)+s;
        }
        else s++;
    }
    for(int i=0;i