剑指offer

2018-3-13

请实现一个函数按照之字形打印二叉树

思路：两个栈

import java.util.*;

/*
public class TreeNode {
    int val = 0;
    TreeNode left = null;
    TreeNode right = null;

    public TreeNode(int val) {
        this.val = val;

    }

}
*/
public class Solution {
    public ArrayList<ArrayList<Integer> > Print(TreeNode pRoot) {
        ArrayList<ArrayList<Integer>> res = new ArrayList<>();
        if (pRoot == null) {
            return res;
        }
        Stack<TreeNode> stack1 = new Stack<>();
        Stack<TreeNode> stack2 = new Stack<>();
        stack1.push(pRoot);
        while (!stack1.isEmpty() || !stack2.isEmpty()) {
            ArrayList<Integer> layer = new ArrayList<>();
            while (!stack1.isEmpty()) {
                TreeNode node = stack1.pop();
                layer.add(node.val);
                if (node.left != null) {
                    stack2.push(node.left);
                }
                if (node.right != null) {
                    stack2.push(node.right);
                }
            }
            res.add(layer);
            layer = new ArrayList<>();
            while (!stack2.isEmpty()) {
                TreeNode node = stack2.pop();
                layer.add(node.val);
                if (node.right != null) {
                    stack1.push(node.right);
                }
                if (node.left != null) {
                    stack1.push(node.left);
                }
            }
            if (!layer.isEmpty()) {
                res.add(layer);
            }
        }
        return res;
    }

}

把二叉树打印成多行：从上到下按

import java.util.ArrayList;


/*
public class TreeNode {
    int val = 0;
    TreeNode left = null;
    TreeNode right = null;

    public TreeNode(int val) {
        this.val = val;

    }

}
*/
public class Solution {
    ArrayList<ArrayList<Integer> > Print(TreeNode pRoot) {
    
    }
    
}

层打印二叉树，同一层结点从左至右输出。每一层输出一行。