[LC 105.从前序与中序遍历序列构造二叉树]

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public TreeNode buildTree(int[] preorder, int[] inorder) {
        return build(preorder,0,preorder.length-1,inorder,0,inorder.length-1);
    }

    public TreeNode build(int[] preorder,int preStrat,int preEnd,int[] inorder,int inStrat,int inEnd ){

        if(preStrat>preEnd)
            return null;
        int rootVal = preorder[preStrat];
        int index = 0;
        for(int i=inStrat;i<=inEnd;i++){
            if (inorder[i] == rootVal){
                index = i;
                break;
            }
        }
        TreeNode root = new TreeNode(rootVal);
        int leftSize = index-inStrat;
        root.left = build(preorder, preStrat+1,preStrat+leftSize, inorder,inStrat,index-1 );
        root.right = build(preorder, preStrat+leftSize+1,preEnd, inorder,index+1,inEnd);
        return root;
    }
}