給定一個二叉樹，確定它是否是一個完全二叉樹。

百度百科中對完全二叉樹的定義如下：

若設二叉樹的深度為 h，除第 h 層外，其它各層 (1～h-1) 的結點數都達到最大個數，第 h 層所有的結點都連續集中在最左邊，這就是完全二叉樹。（注：第 h 層可能包含 1~2h個節點。）

來源：力扣（LeetCode）
連結：https://leetcode-cn.com/problems/check-completeness-of-a-binary-tree
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class Solution {


    private Info solve(TreeNode root) {
        if (root == null) {
            return new Info(true, true, 0);
        }
        Info left = solve(root.left);
        Info right = solve(root.right);

        if (left.height == right.height) {
            return new Info(left.ok && right.ok && left.isFull, left.isFull && right.isFull, left.height + 1);
        } else if (left.height == right.height + 1) {
            return new Info(left.ok && right.ok && right.isFull, false, left.height + 1);
        } else {
            return new Info(false, false, Math.max(left.height, right.height) + 1);
        }
    }


    public boolean isCompleteTree(TreeNode root) {
        if (root == null) {
            return true;
        }
        return solve(root).ok;
    }
}

class Info {
    boolean ok;
    boolean isFull;
    int height;

    public Info(boolean ok, boolean isFull, int height) {
        this.ok = ok;
        this.isFull = isFull;
        this.height = height;
    }
}


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;
    }
}