lintcode--650. Find Leaves of Binary Tree

描述

给定一个二叉树，像这样收集树节点：收集并移除所有叶子，重复，直到树为空。

样例

Given binary tree:
    1
   / \
  2   3
 / \     
4   5    
Returns [[4, 5, 3], [2], [1]].

代码

这道题可以采用遍历的方式收集叶子节点，并删除。

/**
 * Definition of TreeNode:
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left, right;
 *     public TreeNode(int val) {
 *         this.val = val;
 *         this.left = this.right = null;
 *     }
 * }
 */


public class Solution {
    /*
     * @param root: the root of binary tree
     * @return: collect and remove all leaves
     */
    public List<List<Integer>> findLeaves(TreeNode root) {
        // write your code here
        List<List<Integer>> result=new LinkedList<>();
        if(root==null){
            return result;
        }
        while(root!=null){
            List<Integer> list=new LinkedList<>();
            root=getLeave(root, list);
            result.add(list);
        }
        return result;
    }
    private TreeNode getLeave(TreeNode root,List<Integer> list){
        if(root==null){
            return null;
        }
        if(root.left==null&&root.right==null){
            list.add(root.val);
            return null;
        }
        root.left=getLeave(root.left, list);
        root.right=getLeave(root.right, list);
        return root;
    }
}