105. Construct Binary Tree from Preorder and Inorder Traversal

Posted 2020-10-09 鸵鸟

public class Solution {
    public TreeNode buildTree(int[] preorder, int[] inorder) {
        return buildTree(preorder, 0, preorder.length-1, inorder, 0, inorder.length);
	}
    private TreeNode buildTree(int[] preorder, int l1, int r1, int[] inorder, int l2, int r2){
        if(l1>r1||l2>r2)
            return null;
        int idx=l2;
        while(inorder[idx]!=preorder[l1])
            idx++;
        TreeNode node=new TreeNode(preorder[l1]);
        node.left=buildTree(preorder, l1+1, l1+(idx-l2), inorder, l2, idx-1);
        node.right=buildTree(preorder, l1+(idx-l2)+1, r1, inorder, idx+1, r2);
        return node;
    }
}