题目链接:https://leetcode.com/problems/construct-binary-tree-from-preorder-and-inorder-traversal/
思路:
递归从先序遍历中找到root节点,然后在inorder中找到该节点的左右孩子,
注意递归子节点时的边界与index的关系。
AC 8ms Java:
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
class Solution {
public TreeNode buildTree(int[] preorder, int[] inorder) {
return findRoot(preorder,inorder,0,0,inorder.length-1);
}
public TreeNode findRoot(int[] preorder,int[] inorder,int pStart,int inStart,int inEnd ){
if(pStart>preorder.length-1||inStart>inEnd)
return null;
TreeNode root=new TreeNode(preorder[pStart]);
int index=0;
for(int i=inStart;i<=inEnd;i++){
if(preorder[pStart]==inorder[i]){
index=i;
break;
}
}
root.left=findRoot(preorder,inorder,pStart+1,inStart,index-1);
root.right=findRoot(preorder,inorder,pStart+index-inStart+1,index+1,inEnd);
return root;
}
}