Create main.cpp

Author: JawadSher

17 - Binary Tree Data Structure Problems/30 - Construct Tree From In-Order & Pre-Order/main.cpp

@@ -0,0 +1,34 @@
+class Solution{
+    public:
+    
+    void createMapping(int in[], map<int, int> &nodeToIndex, int n){
+        for(int i = 0; i < n; i++){
+            nodeToIndex[in[i]] = i;
+        }
+        
+    }
+    
+    Node* solve(int in[], int pre[], int &index, int inOrderStart, int inOrderEnd, int n, map<int, int> &nodeToIndex){
+        if(index >= n || inOrderStart > inOrderEnd) return NULL;
+        
+        int element = pre[index++];
+        Node* root = new Node(element);
+        
+        int position = nodeToIndex[element];
+        
+        root->left = solve(in, pre, index, inOrderStart, position - 1, n, nodeToIndex);
+        root->right = solve(in, pre, index, position + 1, inOrderEnd, n, nodeToIndex);
+        
+        return root;
+    }
+    
+    Node* buildTree(int in[],int pre[], int n)
+    {
+       int preOrderIndex = 0;
+       map<int, int> nodeToIndex;
+       createMapping(in, nodeToIndex, n);
+       
+       return solve(in, pre, preOrderIndex, 0, n-1, n, nodeToIndex);
+       
+    }
+};