Find k-th smallest element in BST (Order Statistics in BST)

PROBLEM :

Find k-th smallest element in BST (Order Statistics in BST)
Given root of binary search tree and K as input, find K-th smallest element in BST.



For example, in the following BST, if k = 3, then output should be 10, and if k = 5, then output should be 14.

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SIMPLE c++ IMPLEMENTATION :
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/*  Structure of a Binary Tree
struct Node
{
    int data;
    struct Node* left, *right;
}; */

// root is the root of tree
// no is no of position reached till now , inicially it will be zero
// ele is to save the element at k'th position
// k is the k'th position


 void Kth_smallest_elemet(tree *root,int *no,int *ele,int k)
{
if(root==NULL)
return ;

Kth_smallest_elemet(root->left,&(*no),&(*ele),pos) ;
(*no)++ ;
if((*no)==(pos))
(*ele)=root->info ;
Kth_smallest_elemet(root->right,&(*no),&(*ele),pos) ;
}      

-------------------------------------------------------------------------------
ALTERNATE SOLUTION :
-------------------------------------------------------------------------------
// function returns the element at k'th position


int Kth_smallest_elemet(tree *root,int k)
{
if(root==NULL)
return -1;

int s,i=0 ;
s=size_tree(root) ;

int array[s] ;
inorder_array_fill(root,array,&i) ;

for(i=0;i<s;i++)
{
if(k==1)
return array[i] ;
k-- ;
}
return -1 ;
}

int size_tree(tree* root)
{
if(root==NULL)
return 0 ;

return ((size_tree(root->left))+(size_tree(root->right))+1) ;
}


void inorder_array_fill(tree* root,int a[],int *s)
{
    if(root==NULL)
        return  ;
     
    inorder_array_fill(root->left,a,&(*s)) ;
    a[(*s)++]=root->info ;
    inorder_array_fill(root->right,a,&(*s)) ;
 
}

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