🚀 28-Jul-2020

Author: sureshmangs

competitive programming/leetcode/2020-July-Challenge/Dat-27-Construct Binary Tree from Inorder and Postorder Traversal.cpp

@@ -0,0 +1,48 @@
+Given inorder and postorder traversal of a tree, construct the binary tree.
+
+Note:
+You may assume that duplicates do not exist in the tree.
+
+For example, given
+
+inorder = [9,3,15,20,7]
+postorder = [9,15,7,20,3]
+Return the following binary tree:
+
+    3
+   / \
+  9  20
+    /  \
+   15   7
+
+
+
+
+
+
+/**
+ * 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 {
+public:
+    TreeNode *Tree(vector<int>& in, int x, int y,vector<int>& po,int a,int b){
+        if(x > y || a > b)return nullptr;
+        TreeNode *node = new TreeNode(po[b]);
+        int SI = x;
+        while(node->val != in[SI])SI++;
+        node->left  = Tree(in,x,SI-1,po,a,a+SI-x-1);
+        node->right = Tree(in,SI+1,y,po,a+SI-x,b-1);
+        return node;
+    }
+    TreeNode* buildTree(vector<int>& in, vector<int>& po){
+        return Tree(in,0,in.size()-1,po,0,po.size()-1);
+    }
+};