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build_binary_tree.cpp
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build_binary_tree.cpp
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#include <iostream>
#include <vector>
using namespace std;
typedef struct TreeNode
{
int val;
TreeNode *left, *right;
TreeNode(int x)
{
this->val = x;
this->left = nullptr;
this->right = nullptr;
}
}TreeNode;
class Solution
{
public:
TreeNode* build_binary_tree(vector<int> &inorder, vector<int> &postorder)
{
if(inorder.size()==0)
{
return nullptr;
}
return helper(inorder, postorder, 0, inorder.size()-1, 0, postorder.size()-1);
}
private:
TreeNode* helper(vector<int> &inorder, vector<int> &postorder, int in_start, int in_end, int post_start, int post_end)
{
int i = in_start;
for(;i<=in_end;i++)
{
if (inorder[i] == postorder[post_end])
{
break;
}
}
TreeNode *root = new TreeNode(inorder[i]);
int left_len = i - in_start;
int right_len = in_end - i;
if(left_len>0)
{
root->left = helper(inorder, postorder, in_start, i-1, post_start, post_start+left_len-1);
}
if(right_len>0)
{
root->right = helper(inorder, postorder, i+1, in_end, post_start+left_len, post_end-1);
}
return root;
}
};
int main(int argc, char* argv[])
{
vector<int> inorder = {7, 4, 8, 2, 1, 5, 9, 3, 10, 6};
vector<int> postorder = {7, 8, 4, 2, 9, 5, 10, 6, 3, 1};
Solution s;
TreeNode *root = s.build_binary_tree(inorder, postorder);
return 0;
}