Create construct_tree_from_inorder_postorder.cpp

Author: avidLearnerInProgress

construct_tree_from_inorder_postorder.cpp

@@ -0,0 +1,36 @@
+/**
+ * Definition for a binary tree node.
+ * struct TreeNode {
+ *     int val;
+ *     TreeNode *left;
+ *     TreeNode *right;
+ *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
+ *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
+ *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
+ * };
+ */
+class Solution {
+private:
+    unordered_map<int,int> mp;
+    TreeNode* help(vector<int>& in, vector<int>& pos, int left, int right, int rootidx){
+
+        if(left > right)
+            return NULL;
+        int val = pos[rootidx];
+        TreeNode* node = new TreeNode(val);
+        int p = mp[val];
+        node->right = help(in,pos,p+1,right,rootidx-1);
+        node->left = help(in,pos,left,p-1,rootidx-1-(right-p));
+
+        return node;
+    }
+public:
+    TreeNode* buildTree(vector<int>& in, vector<int>& pos) {
+        for(int i=0;i<in.size();i++){
+            mp[in[i]]=i;
+        }
+
+        return help(in,pos,0,in.size()-1,pos.size()-1);
+    }
+};
+