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Problem 31

Medium

1 · Worked examples

0 / 3

Type an input and write what you think is the output . Each problem is converted to Web Assembly, so any possible input will show the corresponding output. Only correct predictions count.

solution()
returns

2 · Which problem is it?

Locked until you have predicted 3 outputs correctly.

The accepted solution

1struct Node {
2 int val;
3 Node* left;
4 Node* right;
5};
6
7Node* build(const vector<optional<int>>& level) {
8
9 if (level.empty() || !level[0]) {
10 return nullptr;
11 }
12
13 Node* root = new Node{*level[0], nullptr, nullptr};
14
15 queue<Node*> q;
16 q.push(root);
17
18 int i = 1;
19 int n = level.size();
20
21 while (!q.empty() && i < n) {
22
23 Node* node = q.front();
24 q.pop();
25
26 if (level[i]) {
27 node->left = new Node{*level[i], nullptr, nullptr};
28 q.push(node->left);
29 }
30
31 i++;
32
33 if (i < n && level[i]) {
34 node->right = new Node{*level[i], nullptr, nullptr};
35 q.push(node->right);
36 }
37
38 i++;
39 }
40
41 return root;
42}
43
44bool within(Node* node, long lo, long hi) {
45
46 if (!node) {
47 return true;
48 }
49
50 if (node->val <= lo || node->val >= hi) {
51 return false;
52 }
53
54 bool leftOk = within(node->left, lo, node->val);
55 bool rightOk = within(node->right, node->val, hi);
56
57 return leftOk && rightOk;
58}
59
60bool solution(const vector<optional<int>>& level) {
61
62 Node* root = build(level);
63
64 return within(root, LONG_MIN, LONG_MAX);
65}

Names have been stripped. The signature is the only clue you get for free. Compiled as C++20 with the standard headers and using namespace std; already in scope.