L958. 二叉树的完全性检验 java

1. 从1开始当下标，最后节点下标==节点总数？true：false；

/**
 * 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 {
    int size=0,maxs=0;
    public boolean isCompleteTree(TreeNode root) {
        if(root==null) return  true;
        func(root,1);
        return size==maxs;
    }
    public void func(TreeNode node , int index){
        if(node==null) return ;
        size++;
        maxs=Math.max(maxs,index);   
        func(node.left,2*index);
        func(node.right,1+2*index);
   


    }
}

2. 标准BFS，层序遍历，出现空节点后再出现非空节点就不是，其他都是。

/**
 * 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 {
    int size=0,maxs=0;
    public boolean isCompleteTree(TreeNode root) {
        if(root==null) return true;
        int cnt=0;
        Queue<TreeNode> q = new LinkedList<>();
        q.offer(root);
        while(!q.isEmpty()){
            TreeNode cur= q.poll();
            if(cur==null) cnt=1;
            else{
                if(cnt==1) return false;
                q.offer(cur.left);
                q.offer(cur.right);
            }
        }
        return  true;
    }
}