题目
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。
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.LinkedList;
import java.util.Queue;
/*
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> layer = new LinkedList<TreeNode>();
ArrayList<Integer> layerList = new ArrayList<Integer>();
layer.add(pRoot);
int start=0, end=1;
while(!layer.isEmpty()){
TreeNode tmp = layer.remove();
layerList.add(tmp.val);
start++;
if(tmp.left!=null){
layer.add(tmp.left);
}
if(tmp.right!=null) {
layer.add(tmp.right);
}
if(start==end) {
end = layer.size();
start = 0;
result.add(layerList);
layerList = new ArrayList<Integer>();
}
}
return result;
}
}