add buildTree.cpp

Author: kamyu104

C++/buildTreeWithPostOrder.cpp

@@ -0,0 +1,35 @@
+// Time Complexity: O(n)
+// Space Complexity: O(logn)
+
+/**
+ * Definition for binary tree
+ * struct TreeNode {
+ *     int val;
+ *     TreeNode *left;
+ *     TreeNode *right;
+ *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
+ * };
+ */
+class Solution {
+    public:
+        TreeNode *buildTree(vector<int> &inorder, vector<int> &postorder) {
+            return buildTree(begin(inorder), end(inorder), begin(postorder), end(postorder));
+        }
+    private:
+        template<typename InputIterator>
+            TreeNode *buildTree(InputIterator in_first, InputIterator in_last, InputIterator post_first, InputIterator post_last) {
+                if(in_first == in_last)
+                    return NULL;
+                if(post_first == post_last)
+                    return NULL;
+
+                auto root = new TreeNode(*prev(post_last));
+                auto inRootPos = find(in_first, in_last, *prev(post_last));
+                auto leftSize = distance(in_first, inRootPos);
+                root->left = buildTree(in_first, inRootPos, post_first, next(post_first, leftSize));
+                root->right = buildTree(next(inRootPos), in_last, next(post_first, leftSize), prev(post_last));
+
+                return root;
+            }
+
+};

C++/buildTreeWithPreOrder.cpp

@@ -0,0 +1,35 @@
+// Time Complexity: O(n)
+// Space Complexity: O(logn)
+
+/**
+ * Definition for binary tree
+ * 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 buildTree(begin(preorder), end(preorder), begin(inorder), end(inorder));
+        }
+
+    private:
+        template<typename InputIterator>
+            TreeNode* buildTree(InputIterator pre_first, InputIterator pre_last, InputIterator in_first, InputIterator in_last) {
+                if(pre_first == pre_last)
+                    return NULL;
+                if(in_first == in_last)
+                    return NULL;
+
+                auto root = new TreeNode(*pre_first);
+                auto inRootPos = find(in_first, in_last, *pre_first);
+                auto leftSize = distance(in_first, inRootPos);
+                root->left = buildTree(next(pre_first), next(pre_first, leftSize + 1), in_first, inRootPos);
+                root->right = buildTree(next(pre_first, leftSize + 1), pre_last, next(inRootPos), in_last);
+
+                return root;
+            }
+};