Leetcode #105

gistfile1.txt

import java.util.Arrays;
public class Solution {
    public TreeNode buildTree(int[] preorder, int[] inorder) {
        int len = preorder.length;
        if(len == 0){
            return null;
        }
        return buildTreeHelper(preorder, inorder, 0, len-1, 0, len-1);
    }
    public TreeNode buildTreeHelper(int[] preorder, int [] inorder, int ps, int pe, int is, int ie){
        TreeNode root = new TreeNode(preorder[ps]);
        int position = is;
        int len=0;
        while(inorder[position] != root.val && position <= ie){
            position++;
            len++;
        }
        if(position>is)
            root.left = buildTreeHelper(preorder, inorder, ps+1, ps+len, is, position-1);
        if(position<ie)
            root.right = buildTreeHelper(preorder, inorder, ps+len+1, pe, position+1, ie);
        return root;
    }
}