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buildTree.cpp
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buildTree.cpp
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/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
TreeNode* buildTree(vector<int>& preorder, vector<int>& inorder) {
return helper(preorder, inorder, 0, preorder.size()-1, 0, inorder.size()-1);
}
TreeNode *helper(vector<int> &preorder, vector<int> &inorder, int pl, int pr, int il, int ir) {
if (pl > pr || il > ir) return NULL;
int rootVal = preorder[pl];
TreeNode *root = new TreeNode(rootVal);
root->left = NULL;
root->right = NULL;
int middle = il;
for (int i = il; i <= ir; i++) {
if (inorder[i] == rootVal) {
middle = i;
break;
}
}
root->left = helper(preorder, inorder, pl+1, pl+middle-il, il, middle-1);
root->right = helper(preorder, inorder, pl+middle-il+1, pr, middle+1, ir);
return root;
}
};