[leetcode]105. Construct Binary Tree from Preorder and Inorder Traversal

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public TreeNode buildTree(int[] preorder, int[] inorder) {
        return build(preorder,inorder,0,0,inorder.length-1);
    }
    
    public TreeNode build (int[] preorder, int[] inorder, int preL,int inl,int inr){
        if(inl>inr)return null;
        
        int k=0;
        for(int i=0;i<inorder.length;i++){
            if(preorder[preL]==inorder[i]){
                k=i;
                break;
            }
        }
        TreeNode root=new TreeNode(inorder[k]);
        int leftNum=k-inl;
        
        root.left=build(preorder,inorder,preL+1,inl,k-1);
        root.right=build(preorder,inorder,preL+leftNum+1,k+1,inr);
        
        return root;
    }
}