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173_BSTIterator.cpp
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173_BSTIterator.cpp
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#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using pii = pair<int, int>;
#define endl "\n"
#define fast_io ios::sync_with_stdio(false); cin.tie(0);
#define all(x) begin(x), end(x)
#define debug(x) cerr <<"Line "<< __LINE__ <<" : "<< #x " = "<< x <<endl;
template<typename T, typename TT>
ostream& operator<<(ostream &os, const pair<T, TT> &t) { return os<<"("<<t.first<<", "<<t.second<<")"; }
template<typename T>
ostream& operator<<(ostream& os, const vector<T> &t) { for(auto& i: t) os<<i<<" "; return os; }
/**
* Definition for a binary tree node.
**/
struct TreeNode {
int val;
TreeNode *left;
TreeNode *right;
TreeNode(int x) : val(x), left(NULL), right(NULL) {}
~TreeNode() {
if(left) {
delete left;
left = nullptr;
}
if(right) {
delete right;
right = nullptr;
}
}
};
class BSTIterator {
// stack helps us controlling recursion
stack<TreeNode*> s;
// push all nodes along left path withing its subtree
void leftPush(TreeNode* root) {
while(root) {
s.push(root);
root = root->left;
}
}
public:
BSTIterator(TreeNode* root) {
// initialize with root ans its left....s
leftPush(root);
}
/** @return the next smallest number */
int next() {
// validity check only
assert(!s.empty());
//this node is surely desired next smallest node
TreeNode* smallest = s.top();
s.pop();
// only pushes if it has a right subtree
leftPush(smallest->right);
return smallest->val;
}
/** @return whether we have a next smallest number */
bool hasNext() {
// if stack contains at least one node then we'll be able to process it
return !s.empty();
}
~BSTIterator() {
while(hasNext()) s.pop();
}
};
/**
* Problem : https://leetcode.com/problems/binary-search-tree-iterator/
* Solution : https://leetcode.com/articles/binary-search-tree-iterator/
*
* Your BSTIterator object will be instantiated and called as such:
* BSTIterator* obj = new BSTIterator(root);
* int param_1 = obj->next();
* bool param_2 = obj->hasNext();
*/
void testIterator(BSTIterator* bst_iterator) {
// provides sorted sequence
while(bst_iterator->hasNext()) {
cout << bst_iterator->next() << endl;
}
}
int main(int argc, char** argv) {
fast_io
// generate a tree like structure
TreeNode* root = new TreeNode(7);
root->left = new TreeNode(3);
root->right = new TreeNode(15);
root->right->left = new TreeNode(9);
root->right->right = new TreeNode(20);
// Construct an iterator object
BSTIterator* bst_iterator = new BSTIterator(root);
// Code Testing
testIterator(bst_iterator);
// free up memory
delete bst_iterator;
bst_iterator = nullptr;
delete root;
root = nullptr;
return 0;
}