【剑指Offer】重建二叉树

题目

输入某二叉树的前序遍历和中序遍历的结果，请重建出该二叉树。假设输入的前序遍历和中序遍历的结果中都不含重复的数字。例如输入前序遍历序列{1,2,4,7,3,5,6,8}和中序遍历序列{4,7,2,1,5,3,8,6}，则重建出二叉树并输出它的头结点。

实现

public class TreeNode {
    int val;
    TreeNode left;
    TreeNode right;
    TreeNode(int x) { val = x; }
}

public TreeNode reConstructBinaryTree(int[] pre, int[] in) {
    return reConstructBinaryTree(pre, in, 0, pre.length - 1, 0, in.length - 1);
}

private TreeNode reConstructBinaryTree(int[] pre, int[] in, int startPreorder, int endPreorder, int startInorder, int endInorder){
    if (startPreorder > endPreorder || startInorder > endInorder)
        return null;

    TreeNode node = new TreeNode(pre[startPreorder]);

    for (int i = startInorder; i <= endInorder; i++){
        if (in[i] == pre[startPreorder]){
            int leftLength = i - startInorder;
            node.left = reConstructBinaryTree(pre, in, startPreorder + 1, startPreorder + leftLength, startInorder, i - 1);
            node.right = reConstructBinaryTree(pre, in, startPreorder + leftLength + 1, endPreorder, i + 1, endInorder);
            break;
        }
    }

    return node;
}