剑指 从上到下打印二叉树

剑指 Offer 32 - I. 从上到下打印二叉树

java

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {

    public int[] levelOrder(TreeNode root) {
        if(root == null) return new int[0];
        Queue<TreeNode> queue = new LinkedList<>();
        ArrayList<Integer> res =  new ArrayList<>(); 
       return forEacher( root,queue ,res);

    }
    int[] forEacher(TreeNode root,Queue<TreeNode> queue ,ArrayList<Integer> res){
        queue.add(root);
        while(!queue.isEmpty()){
            TreeNode tmp = queue.poll();
            res.add(tmp.val);
            if(tmp.left!=null) queue.add(tmp.left);
            if(tmp.right!=null) queue.add(tmp.right);
        }
        int[] d = new int[res.size()];
        for(int i = 0;i<res.size();i++){
            d[i] = res.get(i);
        }
        return d;
    }
        
}

剑指 Offer 32 - II. 从上到下打印二叉树 II

java

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public List<List<Integer>> levelOrder(TreeNode root) {
        
        Queue<TreeNode> queue = new LinkedList<>();
        List<List<Integer>> res =  new ArrayList<>(); 
        if(root != null) queue.add(root);
        while(!queue.isEmpty()){
            List<Integer> node = new ArrayList<>();
            for(int i=queue.size();i>0;i--){
                TreeNode tmp = queue.poll();
                node.add(tmp.val);
                if(tmp.left!=null) queue.add(tmp.left);
                if(tmp.right!=null) queue.add(tmp.right);
            }
            res.add(node);
            
        }
        return res;
    }
}

剑指 Offer 32 - III. 从上到下打印二叉树 III

java

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public List<List<Integer>> levelOrder(TreeNode root) {
        
        Queue<TreeNode> queue = new LinkedList<>();
        List<List<Integer>> res =  new ArrayList<>(); 
        if(root != null) queue.add(root);
        while(!queue.isEmpty()){
            List<Integer> node = new ArrayList<>();
            for(int i=queue.size();i>0;i--){
                TreeNode tmp = queue.poll();
                node.add(tmp.val);
                if(tmp.left!=null) queue.add(tmp.left);
                if(tmp.right!=null) queue.add(tmp.right);
            }
            res.add(node);
            
        }
        return res;
    }
}