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binary-search-tree-iterator.js
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binary-search-tree-iterator.js
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// 173. Binary Search Tree Iterator
// Medium
// Implement an iterator over a binary search tree (BST). Your iterator will be initialized with the root node of a BST.
// Calling next() will return the next smallest number in the BST.
// Example:
// BSTIterator iterator = new BSTIterator(root);
// iterator.next(); // return 3
// iterator.next(); // return 7
// iterator.hasNext(); // return true
// iterator.next(); // return 9
// iterator.hasNext(); // return true
// iterator.next(); // return 15
// iterator.hasNext(); // return true
// iterator.next(); // return 20
// iterator.hasNext(); // return false
// Note:
// next() and hasNext() should run in average O(1) time and uses O(h) memory, where h is the height of the tree.
// You may assume that next() call will always be valid, that is, there will be at least a next smallest number in the BST when next() is called.
/**
* Definition for a binary tree node.
* function TreeNode(val, left, right) {
* this.val = (val===undefined ? 0 : val)
* this.left = (left===undefined ? null : left)
* this.right = (right===undefined ? null : right)
* }
*/
/**
* @param {TreeNode} root
*/
var BSTIterator = function(root) {
this.allNodes = [];
dfs(root, this.allNodes);
this.curIdx = 0;
};
function dfs (root, allNodes) {
if(!root) return
dfs(root.left, allNodes)
allNodes.push(root.val)
dfs(root.right, allNodes)
}
/**
* @return the next smallest number
* @return {number}
*/
BSTIterator.prototype.next = function() {
const curNode = this.allNodes[this.curIdx]
this.curIdx++;
return curNode;
};
/**
* @return whether we have a next smallest number
* @return {boolean}
*/
BSTIterator.prototype.hasNext = function() {
return this.curIdx < this.allNodes.length
};
/**
* Your BSTIterator object will be instantiated and called as such:
* var obj = new BSTIterator(root)
* var param_1 = obj.next()
* var param_2 = obj.hasNext()
*/