TreeNode* buildTreeUtil(int iBegin, int iEnd, int pEnd, vector<int>& inorder, vector<int>& postorder) {
if (iBegin > iEnd) return NULL;
TreeNode* root = new TreeNode(postorder[pEnd]);
int i = iBegin;
for ( ; i <= iEnd && inorder[i] != root->val; i++);
root->left = buildTreeUtil(iBegin, i - 1, pEnd + i - 1 - iEnd, inorder, postorder);
root->right = buildTreeUtil(i + 1, iEnd, pEnd - 1, inorder, postorder);
return root;
}
TreeNode *buildTreeUtil(vector<int> &preorder, int &preid, vector<int> &inorder, int l, int r){
if(l>r)return NULL;
if(preid >= preorder.size())return NULL;
if(l==r){
preid++;
return new TreeNode(inorder[l]);
}
TreeNode *root = new TreeNode(preorder[preid]);
int i;
for(i=l;i<=r;i++){
if(inorder[i] == preorder[preid]){
preid++;
break;
}
}
root->left = buildTreeUtil(preorder, preid, inorder, l, i-1);
root->right = buildTreeUtil(preorder, preid, inorder, i+1, r);
return root;
}
TreeNode *buildTree(vector<int> &preorder, vector<int> &inorder) {
int preid = 0;
return buildTreeUtil(preorder, preid, inorder, 0, inorder.size()-1);
}
TreeNode* buildTree(vector<int>& inorder, vector<int>& postorder) {
if (inorder.empty()) return NULL;
return buildTreeUtil(0, inorder.size() - 1, postorder.size() - 1, inorder, postorder);
}
