Inorder Successor - Amazon Top Interview Questions

Problem Statement :

Given a binary search tree root containing unique values, and an integer t, return the value of the inorder successor of t. That is, return the smallest value greater than t in the tree.

Note: you can assume that the inorder successor exists.

Bonus: solve it in \mathcal{O}(h)O(h) time and \mathcal{O}(1)O(1) space where h is the height of the tree.


n ≤ 100,000 where n is the number of nodes in root

Example 1


root = [2, [0, null, [1, null, null]], [3, null, [4, null, null]]]
t = 2



Example 2


root = [2, [0, null, [1, null, null]], [3, null, [4, null, null]]]
t = 1



Solution :


                        Solution in C++ :

 * class Tree {
 *     public:
 *         int val;
 *         Tree *left;
 *         Tree *right;
 * };
int solve(Tree* root, int t) {
    int ans = INT_MAX;
    while (root != NULL) {
        if (root->val > t) {
            ans = min(ans, root->val);
            root = root->left;
        } else {
            root = root->right;
    return ans;

                        Solution in Python : 
# class Tree:
#     def __init__(self, val, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def solve(self, root, t):

        self.max_ele = float("inf")
        self.traverse(root, t)
        return self.max_ele

    def traverse(self, root, t):
        if not root:
        if root.val <= t:
            self.traverse(root.right, t)
            self.max_ele = min(self.max_ele, root.val)
            self.traverse(root.left, t)

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