[Link] https://leetcode.com/problems/recover-a-tree-from-preorder-traversal/
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#include <bits/stdc++.h>
/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode() : val(0), left(nullptr), right(nullptr) {}
* TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
* TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
* };
*/
class Solution {
public:
vector<pair<int,int>> nodes;
TreeNode* div_con(int l, int r) {
if(l == r) return new TreeNode(nodes[l].first);
else if(l+1 == r) {
TreeNode *child_node = new TreeNode(nodes[r].first);
return new TreeNode(nodes[l].first, child_node, nullptr);
}
int top_depth = nodes[l].second;
vector<int> next_nodes;
for(int i = l+1; i <= r; i++) {
if(nodes[i].second == top_depth + 1) next_nodes.push_back(i);
}
if(next_nodes.size() == 1) {
return new TreeNode(nodes[l].first, div_con(next_nodes[0], r), nullptr);
} else if(next_nodes.size() == 2) {
return new TreeNode(nodes[l].first,div_con(next_nodes[0], next_nodes[1] - 1), div_con(next_nodes[1], r));
}
return new TreeNode(nodes[l].first);
}
TreeNode* recoverFromPreorder(string s) {
int i = 0, depth = 0, tot = 0;
string str;
while(i < s.size()) {
depth = 0; str = "";
while(s[i]=='-') { depth++; i++; }
while(i < s.size() && s[i]!='-') str+=s[i++];
int node_val = stoi(str);
nodes.push_back({ node_val, depth });
TreeNode* node = new TreeNode(node_val);
tot++;
}
return div_con(0, tot - 1);
}
};