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[LeetCode]105 Construct Binary Tree from Preorder and Inorder Traversal
https://oj.leetcode.com/problems/construct-binary-tree-from-preorder-and-inorder-traversal/
http://blog.csdn.net/linhuanmars/article/details/24389549
/**
* Definition for binary tree
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
public class Solution {
public TreeNode buildTree(int[] preorder, int[] inorder)
{
int len = preorder.length;
Map<Integer, Integer> inmap = new HashMap<>();
for (int i = 0 ; i < len ; i ++)
{
inmap.put(inorder[i], i);
}
return help(preorder, 0, len - 1, inmap, 0, len - 1);
}
private TreeNode help(int[] preorder, int ps, int pe, Map<Integer, Integer> inmap, int is, int ie)
{
if (ps > pe || is > ie)
return null;
// Root is preorder[ps];
TreeNode root = new TreeNode(preorder[ps]);
int inpos = inmap.get(root.val);
int leftnodes = inpos - is; // How many nodes on the left of root.
root.left = help(preorder, ps + 1, ps + leftnodes, inmap, is, inpos - 1);
root.right = help(preorder, ps + leftnodes + 1, pe, inmap, inpos + 1, ie);
return root;
}
}[LeetCode]105 Construct Binary Tree from Preorder and Inorder Traversal
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