重拾算法之剑指Offier——重建二叉树

剑指Offier——重建二叉树

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。

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

public TreeNode BuildTree(int [] pre, int [] in, int preSt, int preEn, int inSt, int inEn){

if(preSt > preEn || inSt > inEn){
return null;
}

TreeNode treeNode = new TreeNode(pre[preSt]);

for (int i=inSt; i<=inEn; i++){
if(pre[preSt] == in[i]){
treeNode.left = BuildTree(pre, in, preSt+1, preEn,  inSt, i-1);
treeNode.right = BuildTree(pre, in, preSt+1+i-inSt,preEn,i+1, inEn);
}
}
return treeNode;

}

}