leetcode-Construct Binary Tree from Preorder and Inorder Traversal
recursive
1 #include <iostream> 2 #include <vector> 3 using namespace std; 4 5 struct TreeNode { 6 int val; 7 TreeNode *left; 8 TreeNode *right; 9 TreeNode(int x) : val(x), left(NULL), right(NULL) {} 10 }; 11 12 class Solution { 13 public: 14 typedef vector<int>::iterator Iter; 15 TreeNode *buildTree(vector<int> &preorder, vector<int> &inorder) { 16 return buildTreeRecur(inorder.begin(),inorder.end(),preorder.begin(),preorder.end()); 17 } 18 TreeNode* buildTreeRecur(Iter istart,Iter iend,Iter pstart,Iter pend) 19 { 20 if (istart == iend) return NULL; 21 int rootval = *pstart; 22 Iter iterroot = find(istart,iend,rootval); 23 TreeNode *res = new TreeNode(rootval);//建立根节点 24 res->left = buildTreeRecur(istart,iterroot,pstart+1,pstart+1+(iterroot-istart)); 25 res->right = buildTreeRecur(iterroot+1,iend,pstart+1+(iterroot-istart),pend);//vector的end是最后元素还要再下一个！ 26 return res; 27 } 28 }; 29 30 void inorderTraversal(TreeNode* root) 31 { 32 if (root == nullptr) return; 33 inorderTraversal(root->left); 34 cout << root->val << " "; 35 inorderTraversal(root->right); 36 } 37 void preorderTraversal(TreeNode* root) 38 { 39 if (root == nullptr) return; 40 cout << root->val << " "; 41 preorderTraversal(root->left); 42 preorderTraversal(root->right); 43 } 44 int main() 45 { 46 Solution s; 47 vector<int> inorder = {2,4,1,5,3}; 48 vector<int> preorder = { 1,2, 4,3, 5}; 49 TreeNode* root = s.buildTree(preorder,inorder); 50 inorderTraversal(root); 51 cout << endl; 52 preorderTraversal(root); 53 return 0; 54 }
