描述
给定一个二叉树,返回他的后序遍历的序列。
import java.util.ArrayList;
import java.util.List;
public class PostorderTraversalTree {
public class TreeNode {
int val = 0;
TreeNode left = null;
TreeNode right = null;
public TreeNode(int val) {
this.val = val;
}
}
/**
* 代码中的类名、方法名、参数名已经指定,请勿修改,直接返回方法规定的值即可
*
*
* @param root TreeNode类
* @return int整型一维数组
*/
public int[] postorderTraversal (TreeNode root) {
if(null == root){
return new int[]{};
}
List<Integer> listNode = new ArrayList<>();
postorderTraversalImpl(root, listNode);
int[] arr = new int[listNode.size()];
for (int i = 0; i <listNode.size(); i++) {
arr[i] = listNode.get(i);
}
return arr;
}
private void postorderTraversalImpl(TreeNode root, List<Integer> listNode){
TreeNode left = root.left;
TreeNode right = root.right;
if(left != null){
postorderTraversalImpl(left,listNode);
}
if(right != null){
postorderTraversalImpl(right,listNode);
}
listNode.add(root.val);
}
public static void main(String[] args) {
}
}