My java solution


  • 0
    T
        /**
     * Definition for binary tree
     * public class TreeNode {
     *     int val;
     *     TreeNode left;
     *     TreeNode right;
     *     TreeNode(int x) { val = x; }
     * }
     */
    public class Solution {
        public TreeNode buildTree(int[] preorder, int[] inorder) {
            if (preorder.length == 0) return null;
            return recursive(preorder, inorder, 0, preorder.length-1, 0, preorder.length-1);
        }
        
        TreeNode recursive(int[] preorder, int [] inorder, int start1, int end1, int start2 , int end2) {
            int rootVal = preorder[start1];
            int idx = search(inorder, rootVal);
            
            TreeNode n = new TreeNode(rootVal);
                        int len = idx - start2;
    
            if (idx > start2) {
                n.left = recursive(preorder, inorder, start1+1, start1+len, start2, idx-1);
            }
            
            if (idx < end2) {
                n.right = recursive(preorder, inorder, start1+len+1, end1, idx+1, end2);
            }
            
            return n;
        }
        
        int search(int []a, int val) {
            for(int i=0;i<a.length;i++)
                if (a[i] == val) return i;
            return -1;
        }
    }

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