题目
请实现一个函数按照之字形打印二叉树,即第一行按照从左到右的顺序打印,第二层按照从右至左的顺序打印,第三行按照从左到右的顺序打印,其他行以此类推。
分析
思路一:
时间复杂度:o(N)
空间复杂度:o(N)
代码:
import java.util.ArrayList;
import java.util.Stack;
/*
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) {
int layer = 1;
Stack<TreeNode> s1 = new Stack<TreeNode>();//奇数层
s1.push(pRoot);
Stack<TreeNode> s2 = new Stack<TreeNode>();//偶数层
ArrayList<ArrayList<Integer>> list = new ArrayList<ArrayList<Integer>>();
while(!s1.empty()||!s2.empty()) {
//如果是奇数层
if((layer%2)!=0){
ArrayList<Integer> tmp = new ArrayList<Integer>();
while(!s1.empty()){
TreeNode node = s1.pop();
if(node!=null){
tmp.add(node.val);
System.out.print(node.val+" ");
s2.push(node.left);
s2.push(node.right);
}
}
if(!tmp.isEmpty()) {
list.add(tmp);
layer++;
System.out.println();
}
} else{
ArrayList<Integer> tmp = new ArrayList<Integer>();
while(!s2.empty()){
TreeNode node = s2.pop();
if(node!=null){
tmp.add(node.val);
System.out.print(node.val+" ");
s1.push(node.right);
s1.push(node.left);
}
}
if(!tmp.isEmpty()){
list.add(tmp);
layer++;
System.out.println();
}
}
}
return list;
}
}