题目描述
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}，则重建二叉树并返回。
/**
* Definition for binary tree
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
public class Solution {
public TreeNode reConstructBinaryTree(int [] pre,int [] in) {
return build(pre, in, 0, pre.length-1, 0, pre.length);
}
public TreeNode build(int [] pre, int [] in, int preL, int preH, int inL, int inH) {
if (preL > preH) {
return null;
}
TreeNode node = new TreeNode(pre[preL]);
int k;
for (k = 0; pre[preL] != in[k]; k++);
int leftNum = k-inL;
node.left = build(pre, in, preL+1, preL+leftNum, inL, inL+leftNum-1);
node.right = build(pre, in, preL+leftNum+1, preH, inL+leftNum+1, inH);
return node;
}
}