Recursive Method Without Constructing Helper Function.


  • 0

    Similar to the most popular post but without constructing a helper function.

    public TreeNode buildTree(int[] preorder, int[] inorder) {
            int n = preorder.length;
            // Base case.
            if(n == 0) {
                return null;
            }
            // General case.
            int rootVal = preorder[0];
            int rootIndex = 0;
            TreeNode root = new TreeNode(rootVal);
            for(int i = 0; i < n; i++) {
                if(inorder[i] == rootVal) {
                    rootIndex = i;
                    break;
                }
            }
            int leftLength = rootIndex;
            int rightLength = n - 1 - leftLength;
            root.left = buildTree(Arrays.copyOfRange(preorder, 1, 1 + leftLength), Arrays.copyOfRange(inorder, 0, leftLength));
            root.right = buildTree(Arrays.copyOfRange(preorder, 1 + leftLength, n), Arrays.copyOfRange(inorder, rootIndex + 1, n));
            return root;
        }
    

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