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/** 
 * @Author: DaleyZou 
 * @Description: 重建二叉树 
 * 输入某二叉树的前序遍历和中序遍历的结果，请重建出该二叉树。 
 * 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。 
 * 例如输入前序遍历序列{1,2,4,7,3,5,6,8}和中序遍历序列{4,7,2,1,5,3,8,6}，则重建二叉树并返回。 
 * @Date: Created in 7:58 2019/1/29 
 * @Modified By: 
 */ 
public class ConstructBinaryTree_4 { 
 
    public static class TreeNode { 
      int val; 
      TreeNode left; 
      TreeNode right; 
      TreeNode(int x) { val = x; } 
    } 
 
    /** 
     * 缓存中序遍历数组每个值对应的索引 
     */ 
    private Map<Integer, Integer> indexForInOrders = new HashMap<>(); 
 
    public TreeNode reConstructBinaryTree(int [] pre, int [] in) { 
        for (int i = 0; i < in.length; i++){ 
            indexForInOrders.put(in[i], i); 
        } 
 
        return reConstructBinaryTree(pre, 0, pre.length - 1, 0); 
} 
 
    public TreeNode reConstructBinaryTree(int [] pre, int preL, int preR, int inL){ 
        if (preL > preR){ 
            return null; 
        } 
 
        TreeNode root = new TreeNode(pre[preL]); 
 
        int inIndex = indexForInOrders.get(root.val); 
        int leftTreeSize = inIndex - inL; 
 
        root.left = reConstructBinaryTree(pre, preL + 1, preL + leftTreeSize, inL); 
        root.right = reConstructBinaryTree(pre, preL + leftTreeSize + 1, preR, inL + leftTreeSize + 1); 
 
        return root; 
    } 
 
    public static void main(String[] args){ 
        int[] pre = new int[]{1,2,4,7,3,5,6,8}; 
        int[] in = new int []{4,7,2,1,5,3,8,6}; 
        ConstructBinaryTree_4 constructBinaryTree = new ConstructBinaryTree_4(); 
        TreeNode treeNode = constructBinaryTree.reConstructBinaryTree(pre, in); 
        System.out.println(treeNode.val); 
    } 
}