Leet-Code/Construct Binary Tree from PreOrder and PostOrder Traversal at main · Alan9072/Leet-Code · GitHub

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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 {
    public TreeNode constructFromPrePost(int[] preorder, int[] postorder) {
        return construct(preorder,postorder);
    }
    public TreeNode construct(int[] preorder,int[] postorder){

        if(preorder.length == 0 && postorder.length == 0){
            return null;
        }
        TreeNode node = new TreeNode();
        node.val = preorder[0];

        if(preorder.length == 1 && postorder.length == 1 ){
            node.left = null;
            node.right = null;
            return node;
        }

        int splitFactor = preorder[1];
        int index = -1;
        for(int i=0;i<postorder.length;i++){
            if(postorder[i] == splitFactor){
                index = i;
                break;
            }
        }
        //splitting both the arrays into two and passing

        int[] postordFirst = Arrays.copyOfRange(postorder,0,index+1);
        int[] postordSec = Arrays.copyOfRange(postorder,index + 1,postorder.length -1);

        int preFirst[] = Arrays.copyOfRange(preorder,1,postordFirst.length + 1);
        int preSecond[] = Arrays.copyOfRange(preorder,postordFirst.length + 1,preorder.length);

        node.left = construct(preFirst,postordFirst);
        node.right = construct(preSecond,postordSec);

        return node;


    }
}