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35ConstructABinaryTreeFromPostorderAndInOrder.cpp
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35ConstructABinaryTreeFromPostorderAndInOrder.cpp
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#include <bits/stdc++.h>
using namespace std;
struct TreeNode
{
int data;
struct TreeNode* left;
struct TreeNode* right;
TreeNode(int val)
{
data = val;
left = NULL;
right = NULL;
}
};
TreeNode* buildTreeHelper(vector<int>&postOrder,int postStart,int postEnd,vector<int>&inOrder,int inStart,int inEnd,map<int,int> &mp){
if(postStart>postEnd || inStart>inEnd){
return NULL;
}
int rootVal = postOrder[postEnd];
TreeNode* root = new TreeNode(rootVal);
int rootStart = mp[rootVal];
int leftSubTreeSize = rootStart - inStart;
// root->left = buildTreeHelper(postOrder,postStart,)
root->left = buildTreeHelper(postOrder, postStart, postStart + leftSubTreeSize - 1, inOrder, inStart, rootStart - 1, mp);
root->right = buildTreeHelper(postOrder, postStart + leftSubTreeSize, postEnd - 1, inOrder, rootStart + 1, inEnd, mp);
return root;
}
TreeNode* buildTree(vector<int>&postOrder , vector<int>&inOrder){
map<int,int> mp;
for(int i=0;i<inOrder.size();i++){
mp[inOrder[i]] = i;
}
TreeNode* root = buildTreeHelper(postOrder,0,postOrder.size()-1,inOrder,0,inOrder.size()-1,mp);
}
int main(){
struct TreeNode* root = new TreeNode(2);
root->left = new TreeNode(5);
root->left->left = new TreeNode(4);
root->left->left->left = new TreeNode(3);
root->left->left->right = new TreeNode(2);
root->left->right = new TreeNode(5);
root->right = new TreeNode(7);
root->right->left = new TreeNode(9);
root->right->left->right = new TreeNode(2);
root->right->left->right->right = new TreeNode(4);
root->right->left->right->left = new TreeNode(1);
root->right->left->left = new TreeNode(3);
root->right->right = new TreeNode(7);
}