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; }
* }
*/
import java.util.HashMap;
import java.util.Map;
public class Solution {
Map<Integer,Integer>map=new HashMap<>();
public TreeNode reConstructBinaryTree(int [] pre,int [] in) {
for(int i=0;i<in.length;i++)
map.put(in[i],i);
return reConstructBinaryTree(pre,0,pre.length-1,0);
}
public TreeNode reConstructBinaryTree(int[]pre,int preL,int preR,int inL){
if(preL>preR)return null;
TreeNode root=new TreeNode(pre[preL]);
int index=map.get(root.val);
int leftTreeSize=index-inL;
root.left=reConstructBinaryTree(pre,preL+1,preL+leftTreeSize,inL);
root.right=reConstructBinaryTree(pre,preL+leftTreeSize+1,preR,inL+leftTreeSize+1);
return root;
}
}