leetcode105. 从前序与中序遍历序列构造二叉树

class Solution {

    public TreeNode getTree(int leftIn,int rightIn,int leftPre,int rightPre,int[] pre,int[] in) {
        
        if (leftIn > rightIn) return null;

        //求取根节点在中序数组中的下标
        int rootIn = leftIn;
        while (rootIn <= rightIn && pre[leftPre] != in[rootIn]) rootIn++;

        //求取左子树的个数
        int leftNums = rootIn - leftIn;
        
        TreeNode root = new TreeNode(pre[leftPre]);
        root.left = getTree(leftIn,rootIn-1,leftPre+1,(leftPre+1)+leftNums - 1,pre,in);
        root.right = getTree(rootIn+1,rightIn,(leftPre+1)+leftNums,rightPre,pre,in);

        return root;
    }
    public TreeNode buildTree(int[] preorder, int[] inorder) {
        
        return getTree(0,inorder.length-1,0,preorder.length-1,preorder,inorder);

    }
}