105. 从前序与中序遍历序列构造二叉树 --力扣 --JAVA

class Solution {
    public TreeNode buildTree(int[] preorder, int[] inorder) {
        int size = preorder.length;
        Map<Integer,Integer> store = new HashMap<>();
        for (int i = 0; i < inorder.length; i++){
            store.put(inorder[i],i);
        }
        return build(preorder, store,0,0,size - 1);
    }
    private TreeNode build(int[] preorder, Map<Integer,Integer> store, int root,int left,int right){
        if(left > right){
            return null;
        }
        TreeNode node = new TreeNode(preorder[root]);
        int middle = store.get(preorder[root]);
        node.left = build(preorder, store,root + 1, left, middle - 1);
        //middle - left是左子树的长度 1表示下一个节点
        node.right = build(preorder, store,root + middle - left + 1, middle + 1, right);
        return node;
    }
}