从上到下按层打印二叉树,同一层结点从左至右输出。每一层输出一行
- 主要思想:层次遍历、广度优先搜索
- 题目要点:
- 题目要求将二叉树打印成多行,即层次遍历。常规的广度优先遍历在变成层次遍历时,只需记录下每一层的size,另外加个for循环即可。
- 记住bfs的套路很重要。
import java.util.ArrayList;
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 {
ArrayList<ArrayList<Integer> > Print(TreeNode pRoot) {
ArrayList<ArrayList<Integer>> result = new ArrayList<ArrayList<Integer>>();
if (pRoot == null)
return result;
Queue<TreeNode> queue = new LinkedList<TreeNode>();
queue.offer(pRoot);
while (!queue.isEmpty()) {
int size = queue.size();
ArrayList<Integer> curLevel = new ArrayList<Integer>();
for (int i = 0; i < size; i++) {
TreeNode treeNode = queue.poll();
curLevel.add(treeNode.val);
if (treeNode.left != null)
queue.offer(treeNode.left);
if (treeNode.right != null)
queue.offer(treeNode.right);
}
result.add(curLevel);
}
return result;
}
}