Create main.cpp

Author: JawadSher

17 - Binary Tree Data Structure Problems/31 - Binary Tree From In-Order & Post-Order/main.cpp

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+class Solution {
+  public:
+    void createMapping(vector<int> &in, map<int, int> &nodeToIndex, int n){
+        for(int i = 0; i < n; i++){
+            nodeToIndex[in[i]] = i;
+        }
+        
+    }
+    
+    Node* solve(vector<int>&in , vector<int> postorder, int &index, int inOrderStart, int inOrderEnd, int n, map<int, int> &nodeToIndex){
+        if(index < 0 || inOrderStart > inOrderEnd) return NULL;
+        
+        int element = postorder[index--];
+        Node* root = new Node(element);
+        
+        int position = nodeToIndex[element];
+        
+        root->right = solve(in, postorder, index, position + 1, inOrderEnd, n, nodeToIndex);
+        root->left = solve(in, postorder, index, inOrderStart, position - 1, n, nodeToIndex);
+        
+        return root;
+    }
+    // Function to return a tree created from postorder and inoreder traversals.
+    Node* buildTree(vector<int> inorder, vector<int> &postorder) {
+        int n = postorder.size();
+        
+        int postOrderIndex = n-1;
+        map<int, int> nodeToIndex;
+        createMapping(inorder, nodeToIndex, n);
+       
+        return solve(inorder, postorder, postOrderIndex, 0, n-1, n, nodeToIndex);
+    }
+};