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Author: ankitmodanwall

0105-construct-binary-tree-from-preorder-and-inorder-traversal/0105-construct-binary-tree-from-preorder-and-inorder-traversal.java

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+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     int val;
+ *     TreeNode left;
+ *     TreeNode right;
+ *     TreeNode() {}
+ *     TreeNode(int val) { this.val = val; }
+ *     TreeNode(int val, TreeNode left, TreeNode right) {
+ *         this.val = val;
+ *         this.left = left;
+ *         this.right = right;
+ *     }
+ * }
+ */
+class Solution {
+        int preIndex = 0;
+
+    public TreeNode buildTree(int[] preorder, int[] inorder) {
+        return build(preorder, inorder, 0, inorder.length -1);
+    }
+    TreeNode build(int[] preorder, int[] inorder, int start, int end){
+        if(start>end) return null;
+        
+        int rootval = preorder[preIndex++];
+        TreeNode root = new TreeNode(rootval);
+
+        int inIndex = find(inorder, start, end, rootval);
+
+        root.left = build(preorder, inorder, start, inIndex -1);
+        root.right = build(preorder , inorder, inIndex+1, end);
+        return root;
+    }
+
+    int find(int[] arr, int s, int e, int key){
+        for(int i = s; i<=e; i++) {
+            if(arr[i] == key) return i;
+        }
+        return -1;
+    }
+}