[leetcode]Construct Binary Tree from Preorder and Inorder Traversal

Construct Binary Tree from Preorder and Inorder Traversal

 Given preorder and inorder traversal of a tree, construct the binary tree.

Note:
You may assume that duplicates do not exist in the tree.

算法思路：

根据前序序列和中序序列构建树。递归，没难度。

public class Solution {
    public TreeNode buildTree(int[] preorder, int[] inorder) {
        if(preorder == null || inorder == null || preorder.length != inorder.length || preorder.length == 0) return null;
        int val = preorder[0],length = inorder.length;
        int mid = 0;
        for(int i = 0; i < length; i++){
            if(inorder[i] == val){
                mid = i;
                break;
            }
        }
        int[] leftPre = Arrays.copyOfRange(preorder, 1, mid + 1);
        int[] leftIn = Arrays.copyOfRange(inorder, 0, mid);
        int[] rightPre = Arrays.copyOfRange(preorder, mid + 1, length);
        int[] rightIn = Arrays.copyOfRange(inorder, mid + 1, length);
        TreeNode root = new TreeNode(val);
        root.left = buildTree(leftPre, leftIn);
        root.right = buildTree(rightPre,rightIn);
        return root;
    }
}