重建二叉树
根据二叉树的前序遍历和中序遍历的结果,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。
/**
* Definition for binary tree
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
import java.util.HashMap;
public class Solution {
//private Map<Integer, Integer> inOrderNumberIndex = new HashMap<>();
HashMap<Integer, Integer> inOrderNumberIndex = new HashMap<Integer, Integer>();
public TreeNode reConstructBinaryTree(int [] pre,int [] in) {
for (int i = 0; i < in.length; i++) {
inOrderNumberIndex.put(in[i], i);
}
return reConstructBinaryTree(pre, 0, pre.length - 1, in, 0, in.length - 1);
}
private TreeNode reConstructBinaryTree(int [] pre,int preL, int preR,
int [] in, int inL, int inR) {
if (preL > preR) {
return null;
}
TreeNode root = new TreeNode(pre[preL]);
int leftChildSize = inOrderNumberIndex.get(pre[preL]) - inL;
root.left = reConstructBinaryTree(pre, preL + 1, preL + leftChildSize,
in, inL, inL + leftChildSize - 1);
root.right = reConstructBinaryTree(pre, preL + leftChildSize + 1, preR,
in, inL + leftChildSize + 1, inR);
return root;
}
}