Added 105. Construct Binary Tree from Preorder and Inorder Traversal

Author: tarunsinghdev

leetcode/cpp/Tree/105.cpp

@@ -0,0 +1,25 @@
+class Solution {
+    unordered_map<int, int > mp;
+public:
+    TreeNode* buildTree_util(vector<int>& preorder, int pre1, int pre2 , vector<int>& inorder, int i1, int i2) {
+        if(pre1 > pre2 || i1 > i2)
+            return NULL;
+        TreeNode *root = new TreeNode(preorder[pre1]);
+        int diff = mp[preorder[pre1]] - i1;
+        root->left = buildTree_util(preorder, pre1 + 1, pre1+diff, inorder, i1, i1+diff-1);
+        root->right = buildTree_util(preorder, pre1 +diff+1, pre2 , inorder, i1+diff+1, i2);
+        
+        return root;
+    }
+        
+        
+    TreeNode* buildTree(vector<int>& preorder, vector<int>& inorder) {
+        int n = inorder.size();
+        if(n == 0)
+            return NULL;
+        for(int i = 0; i < n; i++)
+            mp[inorder[i]] = i;
+        return buildTree_util(preorder, 0, n-1, inorder,0, n-1);
+        
+    }
+};